Simulation with electrode arrays

ABSTRACT

Some implementations provide an implantable wirelessly powered device for implantation in a patient&#39;s body, the device including: two or more electrode arrays configured to apply at least one electrical pulse to an excitable tissue, each electrode array including at least one electrode; two or more connector contacts, each integrally wired to a particular electrode array, each configured to drive the at least one electrode of the particular electrode array integrally wired thereto with the at least one electrical pulse and to set a polarity for each of the at least one electrode of the particular electrode array integrally wired thereto; a first antenna configured to: receive, from a second antenna and through electrical radiative coupling, an input signal containing electrical energy as well as polarity assignment information, the second antenna located outside the patient&#39;s body; and one or more circuits electrically connected to the first antenna and the connector contacts, the circuits configured to: create the one or more electrical pulses suitable for stimulation of the excitable tissue by using the electrical energy contained in the input signal; program each connector contact to set the polarity for the at least one electrode of the particular electrode array integrally wired thereto based on the polarity assignment information contained in the input signal; and supply the one or more electrical pulses to the connector contacts.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. provisional Patent Application62/004,284, filed May 29, 2014, the disclosure of which is incorporatedby reference in its entirety for all purposes.

TECHNICAL FIELD

This application relates generally to implantable stimulators.

BACKGROUND

Modulation of excitable tissue in the body by electrical stimulation hasbecome an important type of therapy for patients with chronic disablingconditions, including chronic pain, problems of movement initiation andcontrol, involuntary movements, vascular insufficiency, heartarrhythmias and more. A variety of therapeutic intra-body electricalstimulation techniques can treat these conditions. For instance, devicesmay be used to deliver stimulatory signals to excitable tissue, recordvital signs, perform pacing or defibrillation operations, record actionpotential activity from targeted tissue, control drug release fromtime-release capsules or drug pump units, or interface with the auditorysystem to assist with hearing. Typically, such devices utilize asubcutaneous battery operated implantable pulse generator (IPG) toprovide power or other charge storage mechanisms.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a high-level diagram of an example of a wirelessstimulation system.

FIG. 2 depicts a detailed diagram of an example of the wirelessstimulation system.

FIG. 3 is a flowchart showing an example of the operation of thewireless stimulation system.

FIG. 4 is a circuit diagram showing an example of a wireless stimulationdevice.

FIG. 5 is a circuit diagram of another example of a wireless stimulationdevice.

FIG. 6 is a block diagram showing an example of control and feedbackfunctions of a wireless stimulation device.

FIG. 7 is a schematic showing an example of a wireless stimulationdevice with components to implement control and feedback functions.

FIG. 8 is a schematic of an example of a polarity routing switchnetwork.

FIG. 9A is a diagram of an example microwave field stimulator (MFS)operating along with a wireless stimulation device.

FIG. 9B is a diagram of another example MFS operating along with awireless stimulation device.

FIG. 10 is a detailed diagram of an example MFS.

FIG. 11 is a flowchart showing an example process in which the MFStransmits polarity setting information to the wireless stimulationdevice.

FIG. 12 is another flow chart showing an example process in which theMFS receives and processes the telemetry feedback signal to makeadjustments to subsequent transmissions.

FIG. 13 is a schematic of an example implementation of power, signal andcontrol flow on the wireless stimulation device.

FIG. 14A is a diagram of an example of a wireless system for stimulatingexcitable tissue using multiple electrode arrays.

FIG. 14B is a diagram of an example of the wireless system of FIG. 14Athat includes an implantable device with a Y-joint receiver withmultiple connectors each integrally attached to a electrode array.

FIG. 14C is a block diagram illustrating an example of the circuitry ofthe implantable device with the Y-joint receiver.

FIG. 15 shows an example of an electrode assignment for the implantabledevice with Y-joint receiver.

FIG. 16 shows an example of longitudinal currents formed betweenelectrodes of a electrode array connected to the Y-joint receiver.

FIG. 17A shows an example of lateral currents formed between electrodesof two electrode arrays connected to the Y-joint receiver.

FIG. 17B shows an example of a combination of lateral current field andlongitudinal current field formed between electrodes of two electrodearrays connected to a Y-joint receiver.

FIG. 17C shows an example of stimulation zones formed by current fieldsbetween electrodes of two electrode arrays connected to the Y-jointreceiver.

FIG. 17D shows an example of currents between two electrode arrays whenthe two electrode arrays are placed end to end.

FIG. 18A shows an example of an implantable device with a Y-jointreceiver in which the stylet lumen for each electrode array exits at thecentral stem of the Y-joint receiver.

FIG. 18B shows an example of an implantable device with a Y-jointreceiver in which stylet lumens for each electrode array exit at therespective stem and before the central stem of the Y-joint receiver.

FIG. 19A shows an example of a large mouth cannula to fit both electrodearrays of an implantable device with a Y-joint receiver.

FIG. 19B shows examples of two cannulas for the electrode arrays of animplantable device with a Y-joint receiver.

DETAILED DESCRIPTION

In various implementations, systems and methods are disclosed forapplying one or more electrical impulses to targeted excitable tissue,such as nerves, for treating chronic pain, inflammation, arthritis,sleep apnea, seizures, incontinence, pain associated with cancer,incontinence, problems of movement initiation and control, involuntarymovements, vascular insufficiency, heart arrhythmias, obesity, diabetes,craniofacial pain, such as migraines or cluster headaches, and otherdisorders. In certain embodiments, a wireless stimulation device may beused to send electrical energy to targeted nerve tissue by using remoteradio frequency (RF) energy with neither cables nor inductive couplingto power the passive implanted wireless stimulation device. The targetednerves can include, but are not limited to, the spinal cord andsurrounding areas, including the dorsal horn, dorsal root ganglion, theexiting nerve roots, nerve ganglions, the dorsal column fibers and theperipheral nerve bundles leaving the dorsal column and brain, such asthe vagus, occipital, trigeminal, hypoglossal, sacral, coccygeal nervesand the like.

A wireless stimulation system can include an implantable, wirelessstimulation device with one or more electrodes and an enclosure thathouses one or more conductive antennas (for example, dipole or patchantennas), and internal circuitry for frequency waveform and electricalenergy rectification. The system may further comprise an externalcontroller and antenna for sending radio frequency or microwave energyfrom an external source to the implantable device with neither cablesnor inductive coupling to provide power.

In various embodiments, the implantable device is powered wirelessly(and therefore does not require a wired connection) and contains thecircuitry necessary to receive the pulse instructions from a sourceexternal to the body. For example, various embodiments employ internaldipole (or other) antenna configuration(s) to receive RF power throughelectrical radiative coupling. This allows such devices to produceelectrical currents capable of stimulating nerve bundles without aphysical connection to an implantable pulse generator (IPG) or use of aninductive coil. Further descriptions of exemplary wireless systems forproviding neural stimulation to a patient can be found incommonly-assigned, co-pending published PCT applicationsPCT/US2012/23029 filed Jan. 27, 2012, PCT/US2012/32200 filed Apr. 11,2012, PCT/US2012/48903, filed Jan. 28, 2012, PCT/US2012/50633, filedAug. 12, 2012, PCT/US2012/55746, filed Sep. 15, 2012 andPCT/US2013/073326, filed Dec. 5, 2013, the complete disclosures of whichhave been previously incorporated by reference.

FIG. 1 depicts a high-level diagram of an example of a wirelessstimulation system. The wireless stimulation system may include fourmajor components, namely, a programmer module 102, a RF pulse generatormodule 106, a transmit (TX) antenna 110 (for example, a patch antenna,slot antenna, or a dipole antenna), and an implantable wirelessstimulation device 114. The programmer module 102 may be a computerdevice, such as a smart phone, running a software application thatsupports a wireless connection 114, such as Bluetooth®. The applicationcan enable the user to view the system status and diagnostics, changevarious parameters, increase/decrease the desired stimulus amplitude ofthe electrode pulses, and adjust feedback sensitivity of the RF pulsegenerator module 106, among other functions.

The RF pulse generator module 106 may include communication electronicsthat support the wireless connection 104, the stimulation circuitry, andthe battery to power the generator electronics. In some implementations,the RF pulse generator module 106 includes the TX antenna embedded intoits packaging form factor while, in other implementations, the TXantenna is connected to the RF pulse generator module 106 through awired connection 108 or a wireless connection (not shown). The TXantenna 110 may be coupled directly to tissue to create an electricfield that powers the implanted neural stimulator module 114. The TXantenna 110 communicates with the implanted neural stimulator module 114through an RF interface. For instance, the TX antenna 110 radiates an RFtransmission signal that is modulated and encoded by the RF pulsegenerator module 110. The implanted wireless stimulation device ofmodule 114 contains one or more antennas, such as dipole antenna(s), toreceive and transmit through RF interface 112. In particular, thecoupling mechanism between antenna 110 and the one or more antennas onthe implanted wireless stimulation device of module 114 utilizeselectrical radiative coupling and not inductive coupling. In otherwords, the coupling is through an electric field rather than a magneticfield.

Through this electrical radiative coupling, the TX antenna 110 canprovide an input signal to the implanted stimulation module 114. Thisinput signal contains energy and may contain information encodingstimulus waveforms to be applied at the electrodes of the implantedstimulation module 114. In some implementations, the power level of thisinput signal directly determines an applied amplitude (for example,power, current, or voltage) of the one or more electrical pulses createdusing the electrical energy contained in the input signal. Within theimplanted wireless stimulation device 114 are components fordemodulating the RF transmission signal, and electrodes to deliver thestimulation to surrounding neuronal tissue.

The RF pulse generator module 106 can be implanted subcutaneously, or itcan be worn external to the body. When external to the body, the RFgenerator module 106 can be incorporated into a belt or harness designto allow for electric radiative coupling through the skin and underlyingtissue to transfer power and/or control parameters to the implantedwireless stimulation device module 114. In either event, receivercircuit(s) internal to the wireless stimulation device 114 (or connectordevice 1400 shown in FIG. 14A) can capture the energy radiated by the TXantenna 110 and convert this energy to an electrical waveform. Thereceiver circuit(s) may further modify the waveform to create anelectrical pulse suitable for the stimulation of neural tissue.

In some implementations, the RF pulse generator module 106 can remotelycontrol the stimulus parameters (that is, the parameters of theelectrical pulses applied to the neural tissue) and monitor feedbackfrom the wireless stimulation device 114 based on RF signals receivedfrom the implanted wireless stimulation device module 114. A feedbackdetection algorithm implemented by the RF pulse generator module 106 canmonitor data sent wirelessly from the implanted wireless stimulationdevice module 114, including information about the energy that theimplanted wireless stimulation device 114 is receiving from the RF pulsegenerator and information about the stimulus waveform being delivered tothe electrode pads. In order to provide an effective therapy for a givenmedical condition, the system can be tuned to provide the optimal amountof excitation or inhibition to the nerve fibers by electricalstimulation. A closed loop feedback control method can be used in whichthe output signals from the implanted wireless stimulation device 114are monitored and used to determine the appropriate level of neuralstimulation current for maintaining effective neuronal activation, or,in some cases, the patient can manually adjust the output signals in anopen loop control method.

FIG. 2 depicts a detailed diagram of an example of the wirelessstimulation system. As depicted, the programming module 102 may compriseuser input system 202 and communication subsystem 208. The user inputsystem 221 may allow various parameter settings to be adjusted (in somecases, in an open loop fashion) by the user in the form of instructionsets. The communication subsystem 208 may transmit these instructionsets (and other information) via the wireless connection 104, such asBluetooth or Wi-Fi, to the RF pulse generator module 106, as well asreceive data from module 106.

For instance, the programmer module 102, which can be utilized formultiple users, such as a patient's control unit or clinician'sprogrammer unit, can be used to send stimulation parameters to the RFpulse generator module 106. The stimulation parameters that can becontrolled may include pulse amplitude, pulse frequency, and pulse widthin the ranges shown in Table 1. In this context the term pulse refers tothe phase of the waveform that directly produces stimulation of thetissue; the parameters of the charge-balancing phase (described below)can similarly be controlled. The patient and/or the clinician can alsooptionally control overall duration and pattern of treatment.

Stimulation Parameter Table 1 Pulse Amplitude: 0 to 20 mA PulseFrequency: 0 to 10000 Hz Pulse Width: 0 to 2 ms

The RF pulse generator module 114 may be initially programmed to meetthe specific parameter settings for each individual patient during theinitial implantation procedure. Because medical conditions or the bodyitself can change over time, the ability to re-adjust the parametersettings may be beneficial to ensure ongoing efficacy of the neuralmodulation therapy.

The programmer module 102 may be functionally a smart device andassociated application. The smart device hardware may include a CPU 206and be used as a vehicle to handle touchscreen input on a graphical userinterface (GUI) 204, for processing and storing data.

The RF pulse generator module 106 may be connected via wired connection108 to an external TX antenna 110. Alternatively, both the antenna andthe RF pulse generator are located subcutaneously (not shown).

The signals sent by RF pulse generator module 106 to the implantedwireless stimulation device 114 may include both power andparameter-setting attributes in regards to stimulus waveform, amplitude,pulse width, and frequency. The RF pulse generator module 106 can alsofunction as a wireless receiving unit that receives feedback signalsfrom the implanted wireless stimulation device 114. To that end, the RFpulse generator module 106 may contain microelectronics or othercircuitry to handle the generation of the signals transmitted to thedevice 114 as well as handle feedback signals, such as those from thedevice 114. For example, the RF pulse generator module 106 may comprisecontroller subsystem 214, high-frequency oscillator 218, RF amplifier216, a RF switch, and a feedback subsystem 212.

The controller subsystem 214 may include a CPU 230 to handle dataprocessing, a memory subsystem 228 such as a local memory, communicationsubsystem 234 to communicate with programmer module 102 (includingreceiving stimulation parameters from programmer module), pulsegenerator circuitry 236, and digital/analog (D/A) converters 232.

The controller subsystem 214 may be used by the patient and/or theclinician to control the stimulation parameter settings (for example, bycontrolling the parameters of the signal sent from RF pulse generatormodule 106 to the device 114). These parameter settings can affect, forexample, the power, current level, or shape of the one or moreelectrical pulses. The programming of the stimulation parameters can beperformed using the programming module 102, as described above, to setthe repetition rate, pulse width, amplitude, and waveform that will betransmitted by RF energy to the receive (RX) antenna 238, typically adipole antenna (although other types may be used), in the implantedwireless stimulation device 214. The clinician may have the option oflocking and/or hiding certain settings within the programmer interface,thus limiting the patient's ability to view or adjust certain parametersbecause adjustment of certain parameters may require detailed medicalknowledge of neurophysiology, neuroanatomy, protocols for neuralmodulation, and safety limits of electrical stimulation.

The controller subsystem 214 may store received parameter settings inthe local memory subsystem 228, until the parameter settings aremodified by new input data received from the programming module 102. TheCPU 206 may use the parameters stored in the local memory to control thepulse generator circuitry 236 to generate a stimulus waveform that ismodulated by a high frequency oscillator 218 in the range from 300 MHzto 8 GHz (preferably between about 700 MHz and 5.8 GHz and morepreferably between about 800 MHz and 1.3 GHz). The resulting RF signalmay then be amplified by RF amplifier 226 and then sent through an RFswitch 223 to the TX antenna 110 to reach through depths of tissue tothe RX antenna 238.

In some implementations, the RF signal sent by TX antenna 110 may simplybe a power transmission signal used by the wireless stimulation devicemodule 114 to generate electric pulses. In other implementations, atelemetry signal may also be transmitted to the wireless stimulationdevice module 114 to send instructions about the various operations ofthe wireless stimulation device module 114. The telemetry signal may besent by the modulation of the carrier signal (through the skin ifexternal, or through other body tissues if the pulse generator module106 is implanted subcutaneously). The telemetry signal is used tomodulate the carrier signal (a high frequency signal) that is coupledonto the implanted antenna(s) 238 and does not interfere with the inputreceived on the same device to power the wireless stimulation device. Inone embodiment the telemetry signal and powering signal are combinedinto one signal, where the RF telemetry signal is used to modulate theRF powering signal, and thus the wireless stimulation device is powereddirectly by the received telemetry signal; separate subsystems in thewireless stimulation device harness the power contained in the signaland interpret the data content of the signal.

The RF switch 223 may be a multipurpose device such as a dualdirectional coupler, which passes the relatively high amplitude,extremely short duration RF pulse to the TX antenna 110 with minimalinsertion loss while simultaneously providing two low-level outputs tofeedback subsystem 212; one output delivers a forward power signal tothe feedback subsystem 212, where the forward power signal is anattenuated version of the RF pulse sent to the TX antenna 110, and theother output delivers a reverse power signal to a different port of thefeedback subsystem 212, where reverse power is an attenuated version ofthe reflected RF energy from the TX Antenna 110.

During the on-cycle time (when an RF signal is being transmitted towireless stimulation device 114), the RF switch 223 is set to send theforward power signal to feedback subsystem. During the off-cycle time(when an RF signal is not being transmitted to the wireless stimulationdevice module 114), the RF switch 223 can change to a receiving mode inwhich the reflected RF energy and/or RF signals from the wirelessstimulation device module 114 are received to be analyzed in thefeedback subsystem 212.

The feedback subsystem 212 of the RF pulse generator module 106 mayinclude reception circuitry to receive and extract telemetry or otherfeedback signals from the wireless stimulation device 114 and/orreflected RF energy from the signal sent by TX antenna 110. The feedbacksubsystem may include an amplifier 226, a filter 224, a demodulator 222,and an A/D converter 220.

The feedback subsystem 212 receives the forward power signal andconverts this high-frequency AC signal to a DC level that can be sampledand sent to the controller subsystem 214. In this way thecharacteristics of the generated RF pulse can be compared to a referencesignal within the controller subsystem 214. If a disparity (error)exists in any parameter, the controller subsystem 214 can adjust theoutput to the RF pulse generator 106. The nature of the adjustment canbe, for example, proportional to the computed error. The controllersubsystem 214 can incorporate additional inputs and limits on itsadjustment scheme such as the signal amplitude of the reverse power andany predetermined maximum or minimum values for various pulseparameters.

The reverse power signal can be used to detect fault conditions in theRF-power delivery system. In an ideal condition, when TX antenna 110 hasperfectly matched impedance to the tissue that it contacts, theelectromagnetic waves generated from the RF pulse generator 106 passunimpeded from the TX antenna 110 into the body tissue. However, inreal-world applications a large degree of variability may exist in thebody types of users, types of clothing worn, and positioning of theantenna 110 relative to the body surface. Since the impedance of theantenna 110 depends on the relative permittivity of the underlyingtissue and any intervening materials, and also depends on the overallseparation distance of the antenna from the skin, in any givenapplication there can be an impedance mismatch at the interface of theTX antenna 110 with the body surface. When such a mismatch occurs, theelectromagnetic waves sent from the RF pulse generator 106 are partiallyreflected at this interface, and this reflected energy propagatesbackward through the antenna feed.

The dual directional coupler RF switch 223 may prevent the reflected RFenergy propagating back into the amplifier 226, and may attenuate thisreflected RF signal and send the attenuated signal as the reverse powersignal to the feedback subsystem 212. The feedback subsystem 212 canconvert this high-frequency AC signal to a DC level that can be sampledand sent to the controller subsystem 214. The controller subsystem 214can then calculate the ratio of the amplitude of the reverse powersignal to the amplitude of the forward power signal. The ratio of theamplitude of reverse power signal to the amplitude level of forwardpower may indicate severity of the impedance mismatch.

In order to sense impedance mismatch conditions, the controllersubsystem 214 can measure the reflected-power ratio in real time, andaccording to preset thresholds for this measurement, the controllersubsystem 214 can modify the level of RF power generated by the RF pulsegenerator 106. For example, for a moderate degree of reflected power thecourse of action can be for the controller subsystem 214 to increase theamplitude of RF power sent to the TX antenna 110, as would be needed tocompensate for slightly non-optimum but acceptable TX antenna couplingto the body. For higher ratios of reflected power, the course of actioncan be to prevent operation of the RF pulse generator 106 and set afault code to indicate that the TX antenna 110 has little or no couplingwith the body. This type of reflected-power fault condition can also begenerated by a poor or broken connection to the TX antenna. In eithercase, it may be desirable to stop RF transmission when thereflected-power ratio is above a defined threshold, because internallyreflected power can result in unwanted heating of internal components,and this fault condition means the system cannot deliver sufficientpower to the implanted wireless stimulation device and thus cannotdeliver therapy to the user.

The controller 242 of the wireless stimulation device 114 may transmitinformational signals, such as a telemetry signal, through the antenna238 to communicate with the RF pulse generator module 106 during itsreceive cycle. For example, the telemetry signal from the wirelessstimulation device 114 may be coupled to the modulated signal on thedipole antenna(s) 238, during the on and off state of the transistorcircuit to enable or disable a waveform that produces the correspondingRF bursts necessary to transmit to the external (or remotely implanted)pulse generator module 106. The antenna(s) 238 may be connected toelectrodes 254 in contact with tissue to provide a return path for thetransmitted signal. An A/D (not shown) converter can be used to transferstored data to a serialized pattern that can be transmitted on thepulse-modulated signal from the internal antenna(s) 238 of the wirelessstimulation device 114.

A telemetry signal from the implanted wireless stimulation device module114 may include stimulus parameters such as the power or the amplitudeof the current that is delivered to the tissue from the electrodes. Thefeedback signal can be transmitted to the RF pulse generator module 116to indicate the strength of the stimulus at the nerve bundle by means ofcoupling the signal to the implanted RX antenna 238, which radiates thetelemetry signal to the external (or remotely implanted) RF pulsegenerator module 106. The feedback signal can include either or both ananalog and digital telemetry pulse modulated carrier signal. Data suchas stimulation pulse parameters and measured characteristics ofstimulator performance can be stored in an internal memory device withinthe implanted stimulation device 114, and sent on the telemetry signal.The frequency of the carrier signal may be in the range of at 300 MHz to8 GHz (preferably between about 700 MHz and 5.8 GHz and more preferablybetween about 800 MHz and 1.3 GHz).

In the feedback subsystem 212, the telemetry signal can be downmodulated using demodulator 222 and digitized by being processed throughan analog to digital (A/D) converter 220. The digital telemetry signalmay then be routed to a CPU 230 with embedded code, with the option toreprogram, to translate the signal into a corresponding currentmeasurement in the tissue based on the amplitude of the received signal.The CPU 230 of the controller subsystem 214 can compare the reportedstimulus parameters to those held in local memory 228 to verify thewireless stimulation device 114 delivered the specified stimuli totissue. For example, if the wireless stimulation device reports a lowercurrent than was specified, the power level from the RF pulse generatormodule 106 can be increased so that the implanted wireless stimulationdevice 114 will have more available power for stimulation. The implantedwireless stimulation device 114 can generate telemetry data in realtime, for example, at a rate of 8 Kbits per second. All feedback datareceived from the implanted module 114 can be logged against time andsampled to be stored for retrieval to a remote monitoring systemaccessible by the health care professional for trending and statisticalcorrelations.

The sequence of remotely programmable RF signals received by theinternal antenna(s) 238 may be conditioned into waveforms that arecontrolled within the implantable wireless stimulation device 114 by thecontrol subsystem 242 and routed to the appropriate electrodes 254 thatare placed in proximity to the tissue to be stimulated. For instance,the RF signal transmitted from the RF pulse generator module 106 may bereceived by RX antenna 238 and processed by circuitry, such as waveformconditioning circuitry 240, within the implanted wireless stimulationdevice module 114 to be converted into electrical pulses applied to theelectrodes 254 through electrode interface 252. In some implementations,the implanted wireless stimulation device 114 contains between two tosixteen electrodes 254.

The waveform conditioning circuitry 240 may include a rectifier 244,which rectifies the signal received by the RX antenna 238. The rectifiedsignal may be fed to the controller 242 for receiving encodedinstructions from the RF pulse generator module 106. The rectifiersignal may also be fed to a charge balance component 246 that isconfigured to create one or more electrical pulses based such that theone or more electrical pulses result in a substantially zero net chargeat the one or more electrodes (that is, the pulses are charge balanced).The charge-balanced pulses are passed through the current limiter 248 tothe electrode interface 252, which applies the pulses to the electrodes254 as appropriate.

The current limiter 248 insures the current level of the pulses appliedto the electrodes 254 is not above a threshold current level. In someimplementations, an amplitude (for example, current level, voltagelevel, or power level) of the received RF pulse directly determines theamplitude of the stimulus. In this case, it may be particularlybeneficial to include current limiter 248 to prevent excessive currentor charge being delivered through the electrodes, although currentlimiter 248 may be used in other implementations where this is not thecase. Generally, for a given electrode having several square millimeterssurface area, it is the charge per phase that should be limited forsafety (where the charge delivered by a stimulus phase is the integralof the current). But, in some cases, the limit can instead be placed onthe current, where the maximum current multiplied by the maximumpossible pulse duration is less than or equal to the maximum safecharge. More generally, the limiter 248 acts as a charge limiter thatlimits a characteristic (for example, current or duration) of theelectrical pulses so that the charge per phase remains below a thresholdlevel (typically, a safe-charge limit).

In the event the implanted wireless stimulation device 114 receives a“strong” pulse of RF power sufficient to generate a stimulus that wouldexceed the predetermined safe-charge limit, the current limiter 248 canautomatically limit or “clip” the stimulus phase to maintain the totalcharge of the phase within the safety limit. The current limiter 248 maybe a passive current limiting component that cuts the signal to theelectrodes 254 once the safe current limit (the threshold current level)is reached. Alternatively, or additionally, the current limiter 248 maycommunicate with the electrode interface 252 to turn off all electrodes254 to prevent tissue damaging current levels.

A clipping event may trigger a current limiter feedback control mode.The action of clipping may cause the controller to send a thresholdpower data signal to the pulse generator 106. The feedback subsystem 212detects the threshold power signal and demodulates the signal into datathat is communicated to the controller subsystem 214. The controllersubsystem 214 algorithms may act on this current-limiting condition byspecifically reducing the RF power generated by the RF pulse generator,or cutting the power completely. In this way, the pulse generator 106can reduce the RF power delivered to the body if the implanted wirelessstimulation device 114 reports it is receiving excess RF power.

The controller 250 of the stimulator 205 may communicate with theelectrode interface 252 to control various aspects of the electrodesetup and pulses applied to the electrodes 254. The electrode interface252 may act as a multiplex and control the polarity and switching ofeach of the electrodes 254. For instance, in some implementations, thewireless stimulator 106 has multiple electrodes 254 in contact withtissue, and for a given stimulus the RF pulse generator module 106 canarbitrarily assign one or more electrodes to 1) act as a stimulatingelectrode, 2) act as a return electrode, or 3) be inactive bycommunication of assignment sent wirelessly with the parameterinstructions, which the controller 250 uses to set electrode interface252 as appropriate. It may be physiologically advantageous to assign,for example, one or two electrodes as stimulating electrodes and toassign all remaining electrodes as return electrodes.

Also, in some implementations, for a given stimulus pulse, thecontroller 250 may control the electrode interface 252 to divide thecurrent arbitrarily (or according to instructions from pulse generatormodule 106) among the designated stimulating electrodes. This controlover electrode assignment and current control can be advantageousbecause in practice the electrodes 254 may be spatially distributedalong various neural structures, and through strategic selection of thestimulating electrode location and the proportion of current specifiedfor each location, the aggregate current distribution in tissue can bemodified to selectively activate specific neural targets. This strategyof current steering can improve the therapeutic effect for the patient.

In another implementation, the time course of stimuli may be arbitrarilymanipulated. A given stimulus waveform may be initiated at a time Tstart and terminated at a time T final, and this time course may besynchronized across all stimulating and return electrodes; further, thefrequency of repetition of this stimulus cycle may be synchronous forall the electrodes. However, controller 250, on its own or in responseto instructions from pulse generator 106, can control electrodeinterface 252 to designate one or more subsets of electrodes to deliverstimulus waveforms with non-synchronous start and stop times, and thefrequency of repetition of each stimulus cycle can be arbitrarily andindependently specified.

For example, a stimulator having eight electrodes may be configured tohave a subset of five electrodes, called set A, and a subset of threeelectrodes, called set B. Set A might be configured to use two of itselectrodes as stimulating electrodes, with the remainder being returnelectrodes. Set B might be configured to have just one stimulatingelectrode. The controller 250 could then specify that set A deliver astimulus phase with 3 mA current for a duration of 200 us followed by a400 us charge-balancing phase. This stimulus cycle could be specified torepeat at a rate of 60 cycles per second. Then, for set B, thecontroller 250 could specify a stimulus phase with 1 mA current forduration of 500 us followed by a 800 us charge-balancing phase. Therepetition rate for the set-B stimulus cycle can be set independently ofset A, say for example it could be specified at 25 cycles per second.Or, if the controller 250 was configured to match the repetition ratefor set B to that of set A, for such a case the controller 250 canspecify the relative start times of the stimulus cycles to be coincidentin time or to be arbitrarily offset from one another by some delayinterval.

In some implementations, the controller 250 can arbitrarily shape thestimulus waveform amplitude, and may do so in response to instructionsfrom pulse generator 106. The stimulus phase may be delivered by aconstant-current source or a constant-voltage source, and this type ofcontrol may generate characteristic waveforms that are static, e.g. aconstant-current source generates a characteristic rectangular pulse inwhich the current waveform has a very steep rise, a constant amplitudefor the duration of the stimulus, and then a very steep return tobaseline. Alternatively, or additionally, the controller 250 canincrease or decrease the level of current at any time during thestimulus phase and/or during the charge-balancing phase. Thus, in someimplementations, the controller 250 can deliver arbitrarily shapedstimulus waveforms such as a triangular pulse, sinusoidal pulse, orGaussian pulse for example. Similarly, the charge-balancing phase can bearbitrarily amplitude-shaped, and similarly a leading anodic pulse(prior to the stimulus phase) may also be amplitude-shaped.

As described above, the wireless stimulation device 114 may include acharge-balancing component 246. Generally, for constant currentstimulation pulses, pulses should be charge balanced by having theamount of cathodic current should equal the amount of anodic current,which is typically called biphasic stimulation. Charge density is theamount of current times the duration it is applied, and is typicallyexpressed in the units uC/cm². In order to avoid the irreversibleelectrochemical reactions such as pH change, electrode dissolution aswell as tissue destruction, no net charge should appear at theelectrode-electrolyte interface, and it is generally acceptable to havea charge density less than 30 uC/cm². Biphasic stimulating currentpulses ensure that no net charge appears at the electrode after eachstimulation cycle and the electrochemical processes are balanced toprevent net dc currents. The wireless stimulation device 114 may bedesigned to ensure that the resulting stimulus waveform has a net zerocharge. Charge balanced stimuli are thought to have minimal damagingeffects on tissue by reducing or eliminating electrochemical reactionproducts created at the electrode-tissue interface.

A stimulus pulse may have a negative-voltage or current, called thecathodic phase of the waveform. Stimulating electrodes may have bothcathodic and anodic phases at different times during the stimulus cycle.An electrode that delivers a negative current with sufficient amplitudeto stimulate adjacent neural tissue is called a “stimulating electrode.”During the stimulus phase the stimulating electrode acts as a currentsink. One or more additional electrodes act as a current source andthese electrodes are called “return electrodes.” Return electrodes areplaced elsewhere in the tissue at some distance from the stimulatingelectrodes. When a typical negative stimulus phase is delivered totissue at the stimulating electrode, the return electrode has a positivestimulus phase. During the subsequent charge-balancing phase, thepolarities of each electrode are reversed.

In some implementations, the charge balance component 246 uses ablocking capacitor(s) placed electrically in series with the stimulatingelectrodes and body tissue, between the point of stimulus generationwithin the stimulator circuitry and the point of stimulus delivery totissue. In this manner, a resistor-capacitor (RC) network may be formed.In a multi-electrode stimulator, one charge-balance capacitor(s) may beused for each electrode or a centralized capacitor(s) may be used withinthe stimulator circuitry prior to the point of electrode selection. TheRC network can block direct current (DC), however it can also preventlow-frequency alternating current (AC) from passing to the tissue. Thefrequency below which the series RC network essentially blocks signalsis commonly referred to as the cutoff frequency, and in one embodimentthe design of the stimulator system may ensure the cutoff frequency isnot above the fundamental frequency of the stimulus waveform. In thisembodiment as disclosed herein, the wireless stimulator may have acharge-balance capacitor with a value chosen according to the measuredseries resistance of the electrodes and the tissue environment in whichthe stimulator is implanted. By selecting a specific capacitance valuethe cutoff frequency of the RC network in this embodiment is at or belowthe fundamental frequency of the stimulus pulse.

In other implementations, the cutoff frequency may be chosen to be at orabove the fundamental frequency of the stimulus, and in this scenariothe stimulus waveform created prior to the charge-balance capacitor,called the drive waveform, may be designed to be non-stationary, wherethe envelope of the drive waveform is varied during the duration of thedrive pulse. For example, in one embodiment, the initial amplitude ofthe drive waveform is set at an initial amplitude Vi, and the amplitudeis increased during the duration of the pulse until it reaches a finalvalue k*Vi. By changing the amplitude of the drive waveform over time,the shape of the stimulus waveform passed through the charge-balancecapacitor is also modified. The shape of the stimulus waveform may bemodified in this fashion to create a physiologically advantageousstimulus.

In some implementations, the wireless stimulation device module 114 maycreate a drive-waveform envelope that follows the envelope of the RFpulse received by the receiving dipole antenna(s) 238. In this case, theRF pulse generator module 106 can directly control the envelope of thedrive waveform within the wireless stimulation device 114, and thus noenergy storage may be required inside the stimulator itself. In thisimplementation, the stimulator circuitry may modify the envelope of thedrive waveform or may pass it directly to the charge-balance capacitorand/or electrode-selection stage.

In some implementations, the implanted wireless stimulation device 114may deliver a single-phase drive waveform to the charge balancecapacitor or it may deliver multiphase drive waveforms. In the case of asingle-phase drive waveform, for example, a negative-going rectangularpulse, this pulse comprises the physiological stimulus phase, and thecharge-balance capacitor is polarized (charged) during this phase. Afterthe drive pulse is completed, the charge balancing function is performedsolely by the passive discharge of the charge-balance capacitor, whereis dissipates its charge through the tissue in an opposite polarityrelative to the preceding stimulus. In one implementation, a resistorwithin the stimulator facilitates the discharge of the charge-balancecapacitor. In some implementations, using a passive discharge phase, thecapacitor may allow virtually complete discharge prior to the onset ofthe subsequent stimulus pulse.

In the case of multiphase drive waveforms the wireless stimulator mayperform internal switching to pass negative-going or positive-goingpulses (phases) to the charge-balance capacitor. These pulses may bedelivered in any sequence and with varying amplitudes and waveformshapes to achieve a desired physiological effect. For example, thestimulus phase may be followed by an actively driven charge-balancingphase, and/or the stimulus phase may be preceded by an opposite phase.Preceding the stimulus with an opposite-polarity phase, for example, canhave the advantage of reducing the amplitude of the stimulus phaserequired to excite tissue.

In some implementations, the amplitude and timing of stimulus andcharge-balancing phases is controlled by the amplitude and timing of RFpulses from the RF pulse generator module 106, and in others thiscontrol may be administered internally by circuitry onboard the wirelessstimulation device 114, such as controller 250. In the case of onboardcontrol, the amplitude and timing may be specified or modified by datacommands delivered from the pulse generator module 106.

FIG. 3 is a flowchart showing an example of an operation of the wirelessstimulation system. In block 302, the wireless stimulation device 114 isimplanted in proximity to nerve bundles and is coupled to the electricfield produced by the TX antenna 110. That is, the pulse generatormodule 106 and the TX antenna 110 are positioned in such a way (forexample, in proximity to the patient) that the TX antenna 110 iselectrically radiatively coupled with the implanted RX antenna 238 ofthe wireless stimulation device 114. In certain implementations, boththe antenna 110 and the RF pulse generator 106 are locatedsubcutaneously. In other implementations, the antenna 110 and the RFpulse generator 106 are located external to the patient's body. In thiscase, the TX antenna 110 may be coupled directly to the patient's skin.

Energy from the RF pulse generator is radiated to the implanted wirelessstimulation device 114 from the antenna 110 through tissue, as shown inblock 304. The energy radiated may be controlled by thePatient/Clinician Parameter inputs in block 301. In some instances, theparameter settings can be adjusted in an open loop fashion by thepatient or clinician, who would adjust the parameter inputs in block 301to the system.

The implanted wireless stimulation device 114 uses the received energyto generate electrical pulses to be applied to the neural tissue throughthe electrodes 238. For instance, the wireless stimulation device 114may contain circuitry that rectifies the received RF energy andconditions the waveform to charge balance the energy delivered to theelectrodes to stimulate the targeted nerves or tissues, as shown inblock 306. The implanted wireless stimulation device 114 communicateswith the pulse generator 106 by using antenna 238 to send a telemetrysignal, as shown in block 308. The telemetry signal may containinformation about parameters of the electrical pulses applied to theelectrodes, such as the impedance of the electrodes, whether the safecurrent limit has been reached, or the amplitude of the current that ispresented to the tissue from the electrodes.

In block 310, the RF pulse generator 106 detects amplifies, filters andmodulates the received telemetry signal using amplifier 226, filter 224,and demodulator 222, respectively. The A/D converter 230 then digitizesthe resulting analog signal, as shown in 312. The digital telemetrysignal is routed to CPU 230, which determines whether the parameters ofthe signal sent to the wireless stimulation device 114 need to beadjusted based on the digital telemetry signal. For instance, in block314, the CPU 230 compares the information of the digital signal to alook-up table, which may indicate an appropriate change in stimulationparameters. The indicated change may be, for example, a change in thecurrent level of the pulses applied to the electrodes. As a result, theCPU may change the output power of the signal sent to wirelessstimulation device 114 so as to adjust the current applied by theelectrodes 254, as shown in block 316.

Thus, for instance, the CPU 230 may adjust parameters of the signal sentto the wireless stimulation device 114 every cycle to match the desiredcurrent amplitude setting programmed by the patient, as shown in block318. The status of the stimulator system may be sampled in real time ata rate of 8 Kbits per second of telemetry data. All feedback datareceived from the wireless stimulation device 114 can be maintainedagainst time and sampled per minute to be stored for download or uploadto a remote monitoring system accessible by the health care professionalfor trending and statistical correlations in block 318. If operated inan open loop fashion, the stimulator system operation may be reduced tojust the functional elements shown in blocks 302, 304, 306, and 308, andthe patient uses their judgment to adjust parameter settings rather thanthe closed looped feedback from the implanted device.

FIG. 4 is a circuit diagram showing an example of a wireless neuralstimulator, such as wireless stimulation device 114. This examplecontains paired electrodes, comprising cathode electrode(s) 408 andanode electrode(s) 410, as shown. When energized, the charged electrodescreate a volume conduction field of current density within the tissue.In this implementation, the wireless energy is received through a dipoleantenna(s) 238. At least four diodes are connected together to form afull wave bridge rectifier 402 attached to the dipole antenna(s) 238.Each diode, up to 100 micrometers in length, uses a junction potentialto prevent the flow of negative electrical current, from cathode toanode, from passing through the device when said current does not exceedthe reverse threshold. For neural stimulation via wireless power,transmitted through tissue, the natural inefficiency of the lossymaterial may result in a low threshold voltage. In this implementation,a zero biased diode rectifier results in a low output impedance for thedevice. A resistor 404 and a smoothing capacitor 406 are placed acrossthe output nodes of the bridge rectifier to discharge the electrodes tothe ground of the bridge anode. The rectification bridge 402 includestwo branches of diode pairs connecting an anode-to-anode and thencathode to cathode. The electrodes 408 and 410 are connected to theoutput of the charge balancing circuit 246.

FIG. 5 is a circuit diagram of another example of a wireless stimulationdevice 114. The example shown in FIG. 5 includes multiple electrodecontrol and may employ full closed loop control. The wirelessstimulation device includes an electrode array 254 in which the polarityof the electrodes can be assigned as cathodic or anodic, and for whichthe electrodes can be alternatively not powered with any energy. Whenenergized, the charged electrodes create a volume conduction field ofcurrent density within the tissue. In this implementation, the wirelessenergy is received by the device through the dipole antenna(s) 238. Theelectrode array 254 is controlled through an on-board controller circuit242 that sends the appropriate bit information to the electrodeinterface 252 in order to set the polarity of each electrode in thearray, as well as power to each individual electrode. The lack of powerto a specific electrode would set that electrode in a functional OFFposition. In another implementation (not shown), the amount of currentsent to each electrode is also controlled through the controller 242.The controller current, polarity and power state parameter data, shownas the controller output, is be sent back to the antenna(s) 238 fortelemetry transmission back to the pulse generator module 106. Thecontroller 242 also includes the functionality of current monitoring andsets a bit register counter so that the status of total current drawncan be sent back to the pulse generator module 106.

At least four diodes can be connected together to form a full wavebridge rectifier 302 attached to the dipole antenna(s) 238. Each diode,up to 100 micrometers in length, uses a junction potential to preventthe flow of negative electrical current, from cathode to anode, frompassing through the device when said current does not exceed the reversethreshold. For neural stimulation via wireless power, transmittedthrough tissue, the natural inefficiency of the lossy material mayresult in a low threshold voltage. In this implementation, a zero biaseddiode rectifier results in a low output impedance for the device. Aresistor 404 and a smoothing capacitor 406 are placed across the outputnodes of the bridge rectifier to discharge the electrodes to the groundof the bridge anode. The rectification bridge 402 may include twobranches of diode pairs connecting an anode-to-anode and then cathode tocathode. The electrode polarity outputs, both cathode 408 and anode 410are connected to the outputs formed by the bridge connection. Chargebalancing circuitry 246 and current limiting circuitry 248 are placed inseries with the outputs.

FIG. 6 is a block diagram showing an example of control functions 605and feedback functions 630 of an implantable wireless stimulation device600, such as the ones described above or further below. An exampleimplementation may be a wireless stimulation device module 114, asdiscussed above in association with FIG. 2. Control functions 605include functions 610 for polarity switching of the electrodes andfunctions 620 for power-on reset.

Polarity switching functions 610 may employ, for example, a polarityrouting switch network to assign polarities to electrodes 254. Theassignment of polarity to an electrode may, for instance, be one of: acathode (negative polarity), an anode (positive polarity), or a neutral(off) polarity. The polarity assignment information for each of theelectrodes 254 may be contained in the input signal received byimplantable wireless stimulation device 600 through Rx antenna 238 fromRF pulse generator module 106. Because a programmer module 102 maycontrol RF pulse generator module 106, the polarity of electrodes 254may be controlled remotely by a programmer through programmer module102, as shown in FIG. 2.

Power-on reset functions 620 may reset the polarity assignment of eachelectrode immediately on each power-on event. As will be described infurther detail below, this reset operation may cause RF pulse generatormodule 106 to transmit the polarity assignment information to theimplantable wireless stimulation device 600. Once the polarityassignment information is received by the implantable wirelessstimulation device 600, the polarity assignment information may bestored in a register file, or other short-term memory component.Thereafter the polarity assignment information may be used to configurethe polarity assignment of each electrode. If the polarity assignmentinformation transmitted in response to the reset encodes the samepolarity state as before the power-on event, then the polarity state ofeach electrode can be maintained before and after each power-on event.

Feedback functions 630 include functions 640 for monitoring deliveredpower to electrodes 254 and functions 650 for making impedance diagnosisof electrodes 254. For example, delivered power functions 640 mayprovide data encoding the amount of power being delivered fromelectrodes 254 to the excitable tissue and tissue impedance diagnosticfunctions 650 may provide data encoding the diagnostic information oftissue impedance. The tissue impedance is the electrical impedance ofthe tissue as seen between negative and positive electrodes when astimulation current is being released between negative and positiveelectrodes.

Feedback functions 630 may additionally include tissue depth estimatefunctions 660 to provide data indicating the overall tissue depth thatthe input radio frequency (RF) signal from the pulse generator module,such as, for example, RF pulse generator module 106, has penetratedbefore reaching the implanted antenna, such as, for example, RX antenna238, within the wireless implantable neural stimulator 600, such as, forexample, implanted wireless stimulation device 114. For instance, thetissue depth estimate may be provided by comparing the power of thereceived input signal to the power of the RF pulse transmitted by the RFpulse generator 106. The ratio of the power of the received input signalto the power of the RF pulse transmitted by the RF pulse generator 106may indicate an attenuation caused by wave propagation through thetissue. For example, the second harmonic described below may be receivedby the RF pulse generator 106 and used with the power of the inputsignal sent by the RF pulse generator to determine the tissue depth. Theattenuation may be used to infer the overall depth of implantablewireless stimulation device 600 underneath the skin.

The data from blocks 640, 650, and 660 may be transmitted, for example,through Tx antenna 110 to an implantable RF pulse generator 106, asillustrated in FIGS. 1 and 2.

As discussed above in association with FIGS. 1, 2, 4, and 5, animplantable wireless stimulation device 600 may utilize rectificationcircuitry to convert the input signal (e.g., having a carrier frequencywithin a range from about 300 MHz to about 8 GHz) to a direct current(DC) power to drive the electrodes 254. Some implementations may providethe capability to regulate the DC power remotely. Some implementationsmay further provide different amounts of power to different electrodes,as discussed in further detail below.

FIG. 7 is a schematic showing an example of an implantable wirelessstimulation device 700 with components to implement control and feedbackfunctions as discussed above in association with FIG. 6. An RX antenna705 receives the input signal. The RX antenna 705 may be embedded as adipole, microstrip, folded dipole or other antenna configuration otherthan a coiled configuration, as described above. The input signal has acarrier frequency in the GHz range and contains electrical energy forpowering the wireless implantable neural stimulator 700 and forproviding stimulation pulses to electrodes 254. Once received by theantenna 705, the input signal is routed to power management circuitry710. Power management circuitry 710 is configured to rectify the inputsignal and convert it to a DC power source. For example, the powermanagement circuitry 710 may include a diode rectification bridge suchas the diode rectification bridge 402 illustrated in FIG. 4. The DCpower source provides power to stimulation circuitry 711 and logic powercircuitry 713. The rectification may utilize one or more full wave diodebridge rectifiers within the power management circuitry 710. In oneimplementation, a resistor can be placed across the output nodes of thebridge rectifier to discharge the electrodes to the ground of the bridgeanode, as illustrated by the shunt register 404 in FIG. 7.

Turning momentarily to FIG. 8, a schematic of an example of a polarityrouting switch network 800 is shown. As discussed above, the cathodic(−) energy and the anodic energy are received at input 1 (block 722) andinput 2 (block 723), respectively. Polarity routing switch network 800has one of its outputs coupled to an electrode of electrodes 254 whichcan include as few as two electrodes, or as many as sixteen electrodes.Eight electrodes are shown in this implementation as an example.

Polarity routing switch network 800 is configured to either individuallyconnect each output to one of input 1 or input 2, or disconnect theoutput from either of the inputs. This selects the polarity for eachindividual electrode of electrodes 254 as one of: neutral (off), cathode(negative), or anode (positive). Each output is coupled to acorresponding three-state switch 830 for setting the connection state ofthe output. Each three-state switch is controlled by one or more of thebits from the selection input 850. In some implementations, selectioninput 850 may allocate more than one bits to each three-state switch.For example, two bits may encode the three-state information. Thus, thestate of each output of polarity routing switch device 800 can becontrolled by information encoding the bits stored in the register 732,which may be set by polarity assignment information received from theremote RF pulse generator module 106, as described further below.

Returning to FIG. 7, power and impedance sensing circuitry may be usedto determine the power delivered to the tissue and the impedance of thetissue. For example, a sensing resistor 718 may be placed in serialconnection with the anodic branch 714. Current sensing circuit 719senses the current across the resistor 718 and voltage sensing circuit720 senses the voltage across the resistor. The measured current andvoltage may correspond to the actual current and voltage applied by theelectrodes to the tissue.

As described below, the measured current and voltage may be provided asfeedback information to RF pulse generator module 106. The powerdelivered to the tissue may be determined by integrating the product ofthe measured current and voltage over the duration of the waveform beingdelivered to electrodes 254. Similarly, the impedance of the tissue maybe determined based on the measured voltage being applied to theelectrodes and the current being applied to the tissue. Alternativecircuitry (not shown) may also be used in lieu of the sensing resistor718, depending on implementation of the feature and whether bothimpedance and power feedback are measured individually, or combined.

The measurements from the current sensing circuitry 719 and the voltagesensing circuitry 720 may be routed to a voltage controlled oscillator(VCO) 733 or equivalent circuitry capable of converting from an analogsignal source to a carrier signal for modulation. VCO 733 can generate adigital signal with a carrier frequency. The carrier frequency may varybased on analog measurements such as, for example, a voltage, adifferential of a voltage and a power, etc. VCO 733 may also useamplitude modulation or phase shift keying to modulate the feedbackinformation at the carrier frequency. The VCO or the equivalent circuitmay be generally referred to as an analog controlled carrier modulator.The modulator may transmit information encoding the sensed current orvoltage back to RF pulse generator 106.

Antenna 725 may transmit the modulated signal, for example, in the GHzfrequency range, back to the RF pulse generator module 106. In someembodiments, antennas 705 and 725 may be the same physical antenna. Inother embodiments, antennas 705 and 725 may be separate physicalantennas. In the embodiments of separate antennas, antenna 725 mayoperate at a resonance frequency that is higher than the resonancefrequency of antenna 705 to send stimulation feedback to RF pulsegenerator module 106. In some embodiments, antenna 725 may also operateat the higher resonance frequency to receive data encoding the polarityassignment information from RF pulse generator module 106.

Antenna 725 may include a telemetry antenna 725 which may route receiveddata, such as polarity assignment information, to the stimulationfeedback circuit 730. The encoded polarity assignment information may beon a band in the GHz range. The received data may be demodulated bydemodulation circuitry 731 and then stored in the register file 732. Theregister file 732 may be a volatile memory. Register file 732 may be an8-channel memory bank that can store, for example, several bits of datafor each channel to be assigned a polarity. Some embodiments may have noregister file, while some embodiments may have a register file up to 64bits in size. The information encoded by these bits may be sent as thepolarity selection signal to polarity routing switch network 721, asindicated by arrow 734. The bits may encode the polarity assignment foreach output of the polarity routing switch network as one of:+(positive), − (negative), or 0 (neutral). Each output connects to oneelectrode and the channel setting determines whether the electrode willbe set as an anode (positive), cathode (negative), or off (neutral).

Returning to power management circuitry 710, in some embodiments,approximately 90% of the energy received is routed to the stimulationcircuitry 711 and less than 10% of the energy received is routed to thelogic power circuitry 713. Logic power circuitry 713 may power thecontrol components for polarity and telemetry. In some implementations,the power circuitry 713, however, does not provide the actual power tothe electrodes for stimulating the tissues. In certain embodiments, theenergy leaving the logic power circuitry 713 is sent to a capacitorcircuit 716 to store a certain amount of readily available energy. Thevoltage of the stored charge in the capacitor circuit 716 may be denotedas Vdc. Subsequently, this stored energy is used to power a power-onreset circuit 716 configured to send a reset signal on a power-on event.If the wireless implantable neural stimulator 700 loses power for acertain period of time, for example, in the range from about 1millisecond to over 10 milliseconds, the contents in the register file732 and polarity setting on polarity routing switch network 721 may bezeroed. The implantable wireless stimulation device 700 may lose power,for example, when it becomes less aligned with RF pulse generator module106. Using this stored energy, power-on reset circuit 740 may provide areset signal as indicated by arrow 717. This reset signal may causestimulation feedback circuit 730 to notify RF pulse generator module 106of the loss of power. For example, stimulation feedback circuit 730 maytransmit a telemetry feedback signal to RF pulse generator module 106 asa status notification of the power outage. This telemetry feedbacksignal may be transmitted in response to the reset signal andimmediately after power is back on wireless stimulation device 700. RFpulse generator module 106 may then transmit one or more telemetrypackets to implantable wireless stimulation device. The telemetrypackets contain polarity assignment information, which may be saved toregister file 732 and may be sent to polarity routing switch network721. Thus, polarity assignment information in register file 732 may berecovered from telemetry packets transmitted by RF pulse generatormodule 106 and the polarity assignment for each output of polarityrouting switch network 721 may be updated accordingly based on thepolarity assignment information.

The telemetry antenna 725 may transmit the telemetry feedback signalback to RF pulse generator module 106 at a frequency higher than thecharacteristic frequency of an RX antenna 705. In one implementation,the telemetry antenna 725 can have a heightened resonance frequency thatis the second harmonic of the characteristic frequency of RX antenna705. For example, the second harmonic may be utilized to transmit powerfeedback information regarding an estimate of the amount of power beingreceived by the electrodes. The feedback information may then be used bythe RF pulse generator in determining any adjustment of the power levelto be transmitted by the RF pulse generator 106. In a similar manner,the second harmonic energy can be used to detect the tissue depth. Thesecond harmonic transmission can be detected by an external antenna, forexample, on RF pulse generator module 106 that is tuned to the secondharmonic. As a general matter, power management circuitry 710 maycontain rectifying circuits that are non-linear device capable ofgenerating harmonic energies from input signal. Harvesting such harmonicenergy for transmitting telemetry feedback signal could improve theefficiency of implantable wireless stimulation device 700.

FIG. 9A is a diagram of an example implementation of a microwave fieldstimulator (MFS) 902 as part of a stimulation system utilizing animplantable wireless stimulation device 922. In this example, the MFS902 is external to a patient's body and may be placed within in closeproximity, for example, within 3 feet, to an implantable wirelessstimulation device 922. The RF pulse generator module 106 may be oneexample implementation of MFS 902. MFS 902 may be generally known as acontroller module. The implantable wireless stimulation device 922 is apassive device. The implantable wireless stimulation device 922 does nothave its own independent power source, rather it receives power for itsoperation from transmission signals emitted from a TX antenna powered bythe MFS 902, as discussed above.

In certain embodiments, the MFS 902 may communicate with a programmer912. The programmer 912 may be a mobile computing device, such as, forexample, a laptop, a smart phone, a tablet, etc. The communication maybe wired, using for example, a USB or firewire cable. The communicationmay also be wireless, utilizing for example, a bluetooth protocolimplemented by a transmitting blue tooth module 904, which communicateswith the host bluetooth module 914 within the programmer 912.

The MFS 902 may additionally communicate with wireless stimulationdevice 922 by transmitting a transmission signal through a Tx antenna907 coupled to an amplifier 906. The transmission signal may propagatethrough skin and underlying tissues to arrive at the Rx antenna 923 ofthe wireless stimulation device 922. In some implementations, thewireless stimulation device 922 may transmit a telemetry feedback signalback to microwave field stimulator 902.

The microwave field stimulator 902 may include a microcontroller 908configured to manage the communication with a programmer 912 andgenerate an output signal. The output signal may be used by themodulator 909 to modulate a RF carrier signal. The frequency of thecarrier signal may be in the microwave range, for example, from about300 MHz to about 8 GHz, preferably from about 800 MHz to 1.3 GHz. Themodulated RF carrier signal may be amplified by an amplifier 906 toprovide the transmission signal for transmission to the wirelessstimulation device 922 through a TX antenna 907.

FIG. 9B is a diagram of another example of an implementation of amicrowave field stimulator 902 as part of a stimulation system utilizinga wireless stimulation device 922. In this example, the microwave fieldstimulator 902 may be embedded in the body of the patient, for example,subcutaneously. The embedded microwave field stimulator 902 may receivepower from a detached, remote wireless battery charger 932.

The power from the wireless battery charger 932 to the embeddedmicrowave field stimulator 902 may be transmitted at a frequency in theMHz or GHz range. The microwave field stimulator 902 shall be embeddedsubcutaneously at a very shallow depth (e.g., less than 1 cm), andalternative coupling methods may be used to transfer energy fromwireless battery charger 932 to the embedded MFS 902 in the mostefficient manner as is well known in the art.

In some embodiments, the microwave field stimulator 902 may be adaptedfor placement at the epidural layer of a spinal column, near or on thedura of the spinal column, in tissue in close proximity to the spinalcolumn, in tissue located near a dorsal horn, in dorsal root ganglia, inone or more of the dorsal roots, in dorsal column fibers, or inperipheral nerve bundles leaving the dorsal column of the spine.

In this embodiment, the microwave field stimulator 902 shall transmitpower and parameter signals to a passive Tx antenna also embeddedsubcutaneously, which shall be coupled to the RX antenna within thewireless stimulation device 922. The power required in this embodimentis substantially lower since the TX antenna and the RX antenna arealready in body tissue and there is no requirement to transmit thesignal through the skin.

FIG. 10 is a detailed diagram of an example microwave field stimulator902. A microwave field stimulator 902 may include a microcontroller 908,a telemetry feedback module 1002, and a power management module 1004.The microwave field stimulator 902 has a two-way communication schemawith a programmer 912, as well as with a communication or telemetryantenna 1006. The microwave field stimulator 902 sends output power anddata signals through a TX antenna 1008.

The microcontroller 908 may include a storage device 1014, a bluetoothinterface 1013, a USB interface 1012, a power interface 1011, ananalog-to-digital converter (ADC) 1016, and a digital to analogconverter (DAC) 1015. Implementations of a storage device 1014 mayinclude non-volatile memory, such as, for example, static electricallyerasable programmable read-only memory (SEEPROM) or NAND flash memory. Astorage device 1014 may store waveform parameter information for themicrocontroller 908 to synthesize the output signal used by modulator909. The stimulation waveform may include multiple pulses. The waveformparameter information may include the shape, duration, amplitude of eachpulse, as well as pulse repetition frequency. A storage device 1014 mayadditionally store polarity assignment information for each electrode ofthe wireless stimulation device 922. The Bluetooth interface 1013 andUSB interface 1012 respectively interact with either the bluetoothmodule 1004 or the USB module to communicate with the programmer 912.

The communication antenna 1006 and a TX antenna 1008 may, for example,be configured in a variety of sizes and form factors, including, but notlimited to a patch antenna, a slot antenna, or a dipole antenna. The TXantenna 1008 may be adapted to transmit a transmission signal, inaddition to power, to the implantable, passive neural stimulator 922. Asdiscussed above, an output signal generated by the microcontroller 908may be used by the modulator 909 to provide the instructions forcreation of a modulated RF carrier signal. The RF carrier signal may beamplified by amplifier 906 to generate the transmission signal. Adirectional coupler 1009 may be utilized to provide two-way coupling sothat both the forward power of the transmission signal flow transmittedby the TX antenna 1008 and the reverse power of the reflectedtransmission may be picked up by power detector 1022 of telemetryfeedback module 1002. In some implementations, a separate communicationantenna 1006 may function as the receive antenna for receiving telemetryfeedback signal from the wireless stimulation device 922. In someconfigurations, the communication antenna may operate at a higherfrequency band than the TX antenna 1008. For example, the communicationantenna 1006 may have a characteristic frequency that is a secondharmonic of the characteristic frequency of TX antenna 1008, asdiscussed above.

In some embodiments, the microwave field stimulator 902 may additionallyinclude a telemetry feedback module 902. In some implementations, thetelemetry feedback module 1002 may be coupled directly to communicationantenna 1006 to receive telemetry feedback signals. The power detector1022 may provide a reading of both the forward power of the transmissionsignal and a reverse power of a portion of the transmission signal thatis reflected during transmission. The telemetry signal, forward powerreading, and reverse power reading may be amplified by low noiseamplifier (LNA) 1024 for further processing. For example, the telemetrymodule 902 may be configured to process the telemetry feedback signal bydemodulating the telemetry feedback signal to extract the encodedinformation. Such encoded information may include, for example, a statusof the wireless stimulation device 922 and one or more electricalparameters associated with a particular channel (electrode) of thewireless stimulation device 922. Based on the decoded information, thetelemetry feedback module 1002 may be used to calculate a desiredoperational characteristic for the wireless stimulation device 922.

Some embodiments of the MFS 902 may further include a power managementmodule 1004. A power management module 1004 may manage various powersources for the MFS 902. Example power sources include, but are notlimited to, lithium-ion or lithium polymer batteries. The powermanagement module 1004 may provide several operational modes to savebattery power. Example operation modes may include, but are not limitedto, a regular mode, a low power mode, a sleep mode, a deepsleep/hibernate mode, and an off mode. The regular mode providesregulation of the transmission of transmission signals and stimulus tothe wireless stimulation device 922. In regular mode, the telemetryfeedback signal is received and processed to monitor the stimuli asnormal. Low-power mode also provides regulation of the transmission oftransmission signals and stimulus to the electrodes of the wirelessstimulation device. However, under this mode, the telemetry feedbacksignal may be ignored. More specifically, the telemetry feedback signalencoding the stimulus power may be ignored, thereby saving MFS 902overall power consumption. Under sleep mode, the transceiver andamplifier 906 are turned off, while the microcontroller is kept on withthe last saved state in its memory. Under the deep sleep/hibernate mode,the transceiver and amplifier 906 are turned off, while themicrocontroller is in power down mode, but power regulators are on.Under the off mode, all transceiver, microcontroller and regulators areturned off achieving zero quiescent power.

FIG. 11 is a flowchart showing an example process in which the microwavefield stimulator 902 transmits polarity setting information to thewireless stimulation device 922. Polarity assignment information isstored in a non-volatile memory 1102 within the microcontroller 908 ofthe MFS 902. The polarity assignment information may berepresentative-specific and may be chosen to meet the specific need of aparticular patient. Based on the polarity assignment information chosenfor a particular patient, the microcontroller 908 executes a specificroutine for assigning polarity to each electrode of the electrode array.The particular patient has a wireless stimulation device as describedabove.

In some implementations, the polarity assignment procedure includessending a signal to the wireless stimulation device with an initialpower-on portion followed by a configuration portion that encodes thepolarity assignments. The power-on portion may, for example, simplyinclude the RF carrier signal. The initial power-on portion has aduration that is sufficient to power-on the wireless stimulation deviceand allow the device to reset into a configuration mode. Once in theconfiguration mode, the device reads the encoded information in theconfiguration portion and sets the polarity of the electrodes asindicated by the encoded information.

Thus, in some implementations, the microcontroller 908 turns on themodulator 909 so that the unmodulated RF carrier is sent to the wirelessstimulation device 1104. After a set duration, the microcontroller 908automatically initiates transmitting information encoding the polarityassignment. In this scenario, the microcontroller 908 transmits thepolarity settings in the absence of handshake signals from the wirelessstimulation device. Because the microwave field stimulator 902 isoperating in close proximity to wireless stimulation device 922, signaldegradation may not be severe enough to warrant the use of handshakesignals to improve quality of communication.

To transmit the polarity information, the microcontroller 908 reads thepolarity assignment information from the non-volatile memory andgenerates a digital signal encoding the polarity information 1106. Thedigital signal encoding the polarity information may be converted to ananalog signal, for example, by a digital-to-analog (DAC) converter 1112.The analog signal encoding the waveform may modulate a carrier signal atmodulator 909 to generate a configuration portion of the transmissionsignal (1114). This configuration portion of the transmission signal maybe amplified by the power amplifier 906 to generate the signal to betransmitted by antenna 907 (1116). Thereafter, the configuration portionof the transmission signal is transmitted to the wireless stimulationdevice 922 (1118).

Once the configuration portion is transmitted to the wirelessstimulation device, the microcontroller 908 initiates the stimulationportion of the transmission signal. Similar to the configurationportion, the microcontroller 908 generates a digital signal that encodesthe stimulation waveform. The digital signal is converted to an analogsignal using the DAC. The analog signal is then used to modulate acarrier signal at modulator 909 to generate a stimulation portion of thetransmission signal.

In other implementations, the microcontroller 908 initiates the polarityassignment protocol after the microcontroller 908 has recognized apower-on reset signal transmitted by the neural stimulator. The power-onreset signal may be extracted from a feedback signal received bymicrocontroller 908 from the wireless stimulation device 922. Thefeedback signal may also be known as a handshake signal in that italerts the microwave field stimulator 902 of the ready status of thewireless stimulation device 922. In an example, the feedback signal maybe demodulated and sampled to digital domain before the power-on resetsignal is extracted in the digital domain.

FIG. 12 is a flow chart showing an example of the process in which themicrowave field stimulator 902 receives and processes the telemetryfeedback signal to make adjustments to subsequent transmissions.

In some implementations, the microcontroller 908 polls the telemetryfeedback module 1002 (1212). The polling is to determine whether atelemetry feedback signal has been received (1214). The telemetryfeedback signal may include information based on which the MFS 902 mayascertain the power consumption being utilized by the electrodes of thewireless stimulation device 922. This information may also be used todetermine the operational characteristics of the combination system ofthe MFS 902 and the wireless stimulation device 922, as will bediscussed in further detail in association with FIG. 13. The informationmay also be logged by the microwave field stimulator 902 so that theresponse of the patient may be correlated with past treatments receivedover time. The correlation may reveal the patient's individual responseto the treatments the patient has received up to date.

If the microcontroller 908 determines that telemetry feedback module1002 has not yet received telemetry feedback signal, microcontroller 908may continue polling (1212). If the microcontroller 908 determines thattelemetry feedback module 1002 has received telemetry feedback signal,the microcontroller 908 may extract the information contained in thetelemetry feedback signal to perform calculations (1216). The extractionmay be performed by demodulating the telemetry feedback signal andsampling the demodulated signal in the digital domain. The calculationsmay reveal operational characteristics of the wireless stimulationdevice 922, including, for example, voltage or current levels associatedwith a particular electrode, power consumption of a particularelectrode, and/or impedance of the tissue being stimulated through theelectrodes.

Thereafter, in certain embodiments, the microcontroller 908 may storeinformation extracted from the telemetry signals as well as thecalculation results (1218). The stored data may be provided to a userthrough the programmer upon request (1220). The user may be the patient,the doctor, or representatives from the manufacturer. The data may bestored in a non-volatile memory, such as, for example, NAND flash memoryor EEPROM.

In other embodiments, a power management schema may be triggered 1222 bythe microcontroller (908). Under the power management schema, themicrocontroller 908 may determine whether to adjust a parameter ofsubsequent transmissions (1224). The parameter may be amplitude or thestimulation waveform shape. In one implementation, the amplitude levelmay be adjusted based on a lookup table showing a relationship betweenthe amplitude level and a corresponding power applied to the tissuethrough the electrodes. In one implementation, the waveform shape may bepre-distorted to compensate for a frequency response of the microwavefield stimulator 902 and the wireless stimulation device 922. Theparameter may also be the carrier frequency of the transmission signal.For example, the carrier frequency of the transmission signal may bemodified to provide fine-tuning that improves transmission efficiency.

If an adjustment is made, the subsequently transmitted transmissionsignals are adjusted accordingly. If no adjustment is made, themicrocontroller 908 may proceed back to polling the telemetry feedbackmodule 1002 for telemetry feedback signal (1212).

In other implementations, instead of polling the telemetry feedbackmodule 1002, the microcontroller 908 may wait for an interrupt requestfrom telemetry feedback module 1002. The interrupt may be a softwareinterrupt, for example, through an exception handler of the applicationprogram. The interrupt may also be a hardware interrupt, for example, ahardware event and handled by an exception handler of the underlyingoperating system.

FIG. 13 is a schematic of an example implementation of the power, signaland control flow for the wireless stimulation device 922. A DC source1302 obtains energy from the transmission signal received at thewireless stimulation device 922 during the initial power-on portion ofthe transmission signal while the RF power is ramping up. In oneimplementation, a rectifier may rectify the received power-on portion togenerate the DC source 1302 and a capacitor 1304 may store a charge fromthe rectified signal during the initial portion. When the stored chargereaches a certain voltage (for example, one sufficient or close tosufficient to power operations of the wireless stimulation device 922),the power-on reset circuit 1306 may be triggered to send a power-onreset signal to reset components of the neural stimulator. The power-onset signal may be sent to circuit 1308 to reset, for example, digitalregisters, digital switches, digital logic, or other digital components,such as transmit and receive logic 1310. The digital components may alsobe associated with a control module 1312. For example, a control module1312 may include electrode control 252, register file 732, etc. Thepower-on reset may reset the digital logic so that the circuit 1308begins operating from a known, initial state.

In some implementations, the power-on reset signal may subsequentlycause the FPGA circuit 1308 to transmit a power-on reset telemetrysignal back to MFS 902 to indicate that the implantable wirelessstimulation device 922 is ready to receive the configuration portion ofthe transmission signal that contains the polarity assignmentinformation. For example, the control module 1312 may signal the RX/TXmodule 1310 to send the power-on reset telemetry signal to the telemetryantenna 1332 for transmission to MFS 902.

In other implementations, the power-on reset telemetry signal may not beprovided. As discussed above, due to the proximity between MFS 902 andimplantable, passive neural stimulator 922, signal degradation due topropagation loss may not be severe enough to warrant implementations ofhandshake signals from the implantable, passive stimulator 922 inresponse to the transmission signal. In addition, the operationalefficiency of implantable, passive neural stimulator 922 may be anotherfactor that weighs against implementing handshake signals.

Once the FPGA circuit 1308 has been reset to an initial state, the FPGAcircuit 1308 transitions to a configuration mode configured to readpolarity assignments encoded on the received transmission signal duringthe configuration state. In some implementations, the configurationportion of the transmission signal may arrive at the wirelessstimulation device through the RX antenna 1334. The transmission signalreceived may provide an AC source 1314. The AC source 1314 may be at thecarrier frequency of the transmission signal, for example, from about300 MHz to about 8.

Thereafter, the control module 1312 may read the polarity assignmentinformation and set the polarity for each electrode through the analogmux control 1316 according to the polarity assignment information in theconfiguration portion of the received transmission signal. The electrodeinterface 252 may be one example of analog mux control 1316, which mayprovide a channel to a respective electrode of the implantable wirelessstimulation device 922.

Once the polarity for each electrode is set through the analog muxcontrol 1316, the implantable wireless stimulation device 922 is readyto receive the stimulation waveforms. Some implementations may notemploy a handshake signal to indicate the wireless stimulation device922 is ready to receive the stimulation waveforms. Rather, thetransmission signal may automatically transition from the configurationportion to the stimulation portion. In other implementations, theimplantable wireless stimulation device 922 may provide a handshakesignal to inform the MFS 902 that implantable wireless stimulationdevice 922 is ready to receive the stimulation portion of thetransmission signal. The handshake signal, if implemented, may beprovided by RX/TX module 1310 and transmitted by telemetry antenna 1332.

In some implementations, the stimulation portion of the transmissionsignal may also arrive at implantable wireless stimulation devicethrough the RX antenna 1334. The transmission signal received mayprovide an AC source 1314. The AC source 1314 may be at the carrierfrequency of the transmission signal, for example, from about 300 MHz toabout 8 GHz. The stimulation portion may be rectified and conditioned inaccordance with discussions above to provide an extracted stimulationwaveform. The extracted stimulation waveform may be applied to eachelectrode of the implantable wireless stimulation device 922. In someembodiments, the application of the stimulation waveform may beconcurrent, i.e., applied to the electrodes all at once. As discussedabove, the polarity of each electrode has already been set and thestimulation waveform has been applied to the electrodes in accordancewith the polarity settings for the corresponding channel.

In some implementations, each channel of analog mux control 1316 isconnected to a corresponding electrode and may have a reference resistorplaced serially. For example, FIG. 13 shows reference resistors 1322,1324, 1326, and 1328 in a serial connection with a matching channel.Analog mux control 1316 may additionally include a calibration resistor1320 placed in a separate and grounded channel. The calibration resistor1320 is in parallel with a given electrode on a particular channel. Thereference resistors 1322, 1324, 1326, and 1328 as well as thecalibration resistor 1320 may also be known as sensing resistors 718.These resistors may sense an electrical parameter in a given channel, asdiscussed below.

In some configurations, an analog controlled carrier modulator mayreceive a differential voltage that is used to determine the carrierfrequency that should be generated. The generated carrier frequency maybe proportional to the differential voltage. An example analogcontrolled carrier modulator is VCO 733.

In one configuration, the carrier frequency may indicate an absolutevoltage, measured in terms of the relative difference from apre-determined and known voltage. For example, the differential voltagemay be the difference between a voltage across a reference resistorconnected to a channel under measurement and a standard voltage. Thedifferential voltage may be the difference between a voltage acrosscalibration resistor 1320 and the standard voltage. One example standardvoltage may be the ground.

In another configuration, the carrier frequency may reveal an impedancecharacteristic of a given channel. For example, the differential voltagemay be the difference between the voltage at the electrode connected tothe channel under measurement and a voltage across the referenceresistor in series. Because of the serial connection, a comparison ofthe voltage across the reference resistor and the voltage at theelectrode would indicate the impedance of the underlying tissue beingstimulated relative to the impedance of the reference resistor. As thereference resistor's impedance is known, the impedance of the underlyingtissue being stimulated may be inferred based on the resulting carrierfrequency.

For example, the differential voltage may be the difference between avoltage at the calibration resistor and a voltage across the referenceresistor. Because the calibration resistor is placed in parallel to agiven channel, the voltage at the calibration is substantially the sameas the voltage at the given channel. Because the reference resistor isin a serial connection with the given channel, the voltage at thereference resistor is a part of the voltage across the given channel.Thus, the difference between the voltage at the calibration resistor andthe voltage across the reference resistor correspond to the voltage dropat the electrode. Hence, the voltage at the electrode may be inferredbased on the voltage difference.

In yet another configuration, the carrier frequency may provide areading of a current. For example, if the voltage over referenceresistor 1322 has been measured, as discussed above, the current goingthrough reference resistor and the corresponding channel may be inferredby dividing the measured voltage by the impedance of reference resistor1322.

Many variations may exist in accordance with the specifically disclosedexamples above. The examples and their variations may sense one or moreelectrical parameters concurrently and may use the concurrently sensedelectrical parameters to drive an analog controlled modulator device.The resulting carrier frequency varies with the differential of theconcurrent measurements. The telemetry feedback signal may include asignal at the resulting carrier frequency.

The MFS 902 may determine the carrier frequency variation bydemodulating at a fixed frequency and measure phase shift accumulationcaused by the carrier frequency variation. Generally, a few cycles of RFwaves at the resulting carrier frequency may be sufficient to resolvethe underlying carrier frequency variation. The determined variation mayindicate an operation characteristic of the implantable wirelessstimulation device 922. The operation characteristics may include animpedance, a power, a voltage, a current, etc. The operationcharacteristics may be associated with an individual channel. Therefore,the sensing and carrier frequency modulation may be channel specific andapplied to one channel at a given time. Consequently, the telemetryfeedback signal may be time shared by the various channels of theimplantable wireless stimulation device 922.

In one configuration, the analog MUX 1318 may be used by the controllermodule 1312 to select a particular channel in a time-sharing scheme. Thesensed information for the particular channel, for example, in the formof a carrier frequency modulation, may be routed to RX/TX module 1310.Thereafter, RX/TX module 1310 transmits, through the telemetry antenna1332, to the MFS 902, the telemetry feedback encoding the sensedinformation for the particular channel.

FIG. 14A is a diagram of an example of a system for stimulating anexcitable tissue using multiple electrode arrays. The system includes anexternal controller 1402 and an implantable wireless stimulation device1400. External controller 1402 may include a user interface and one ormore antennas. In one configuration, the one or more antennas maytransmit one or more input signals to the implantable device 1400 withneither cable connections nor inductive coupling. For instance, theinput signals may be transmitted via electrical radiative coupling toantenna(s) on the implantable device 1400. The input signals may containelectrical energy to power the implantable device 1400. The inputsignals may also contain polarity assignment information for theelectrodes in electrode arrays 1406A and 1406B on the implantable device1400.

Common portion 1404 may be a central stem that houses antenna(s) forreceiving the input signal as well as the circuits for harvesting theelectrical energy contained in the input signal received. The circuitsmay also generate, using the harvested electrical energy, excitationwaveforms to deliver to electrode arrays 1406A and 1406B. Asillustrated, the implantable device 1400 may include two branches ofelectrode arrays 1406A and 1406B connected to the common portion 1404,with each array 1406A and 1406B including eight (8) electrodes. In thisexample, the excitation waveforms from common portion 1404 provide thecurrent that drives each electrode on both branches.

FIG. 14B is a diagram of an example of the implantable device 1400implemented as a Y-joint receiver with two connectors integrallyattached to electrode array. The implantable device 1400 includes acentral stem 1404 and two branch stems 1414A and 1414B. Central stem1404 includes a tip 1418 that may include a suturing feature foranchoring the central stem 1404 to tissue. Central stem 1404 housesantenna traces 1410A and 1410B as well as circuit 1408. In someexamples, the antenna(s) on the implantable device can be positionedtowards tip 1418. Antenna traces 1410A and 1410B may each be radiativelycoupled to an antenna for receiving input signals from externalcontroller 1402 and/or for sending a telemetry signal to externalcontroller 1402. The input signal may contain electrical energy,excitation waveform parameter information, and polarity assignmentinformation. The input signal may be received on a carrier signal havinga frequency between about 800 KHz and 5.8 GHz. The electrical energy maypower the entire implantable device 1400. Circuit 1408 may includewaveform conditioning circuitry to extract the electrical energy fromthe input signal to power the implantable device. The excitationwaveform may include multiple excitation pulses. The waveform parameterinformation may include the shape, duration, amplitude of each pulse, aswell as pulse repetition frequency. The waveform conditioning circuitrymay additionally create electrical pulses as stimulus pulses based onthe electrical energy and according to the excitation waveform parameterinformation. The stimulus pulses created may be at a frequency of about5 to 20,000 Hz. The polarity assignment information refers to thepolarity assigned to each electrode on a particular electrode array. Thepolarity assignment may be used to program the interfaces to set thecorresponding electrodes on a particular electrode array.

In the example Y-joint implantable device 1400, branch stems 1414A and1414B respectively houses the electrode arrays 1406A and 1406B. Branchstems 1414A and 1414B may converge at fork 1411. Branch stems 1414A and1414B may respectively include cables 1412A and 1412B, each respectivelyconnecting circuit 1408 to the electrode arrays 1406A and 1406B. Thecables may also be referred to as wires. In one example, cables 1412Aand 1412B may be laser welded metal or alloy. For instance, cables 1412Aand 1412B may include MP35N nickel cobalt alloy. The electrode arrays1406A and 1406B each include eight electrodes. The electrode array 1406Aincludes electrodes 1406A-0 to 1406A-7. The electrode array 1406Bincludes electrodes 1406B-0 to 1406B-7. In one instance, each electrodemay be wrapped circumferentially on the exterior wall of a branch stem.Branch stems 1414A and 1414B may extend respectively to tips 1416A and1416B. Tips 1416A and 1416B may each include suturing features (notshown) for anchoring the respective electrode arrays to surroundingtissue.

FIG. 14C is a block diagram of illustrating an example of the circuitryof the implantable device 1400. An RX antenna 705 receives the inputsignal transmitted from external controller 1402. The input signal maybe received at RX antenna 705 via electrical radiative coupling. The RXantenna 705 may be embedded as a dipole, microstrip, folded dipole orother antenna configuration other than a coil configuration. The inputsignal contains electrical energy for powering the wireless implantableneural stimulator 1400 and for providing stimulation pulses toelectrodes 1408A0-7 and 1408B0-7. Antenna 725 may include a telemetryantenna to route received data, such as polarity assignment information,to the device interfaces 1420A and 1420B such that the polarity ofelectrodes on the implantable device can be programmed accordingly.

In one example, the input signal received at antenna 705 is processed atRF interface 1428A of controller 1421. Electrical energy contained inthe input signal may be extracted to power the implantable neuralstimulator device 1400. Stimulation pulses may be created based on theexcitation waveform parameter information contained in the input signal.The created stimulus pulses can be routed to the device interfaces 1420Aand 1420B to drive the respective eight electrodes connected thereto.Description box 1422A shows the schematic for electrode array 1406A. Asillustrated, a capacitor bank 1424A (with eight capacitors) is availablefor the electrode array of eight electrodes, namely 1408A-0 to 1408A-7.A capacitor may provide power to the electrode connected thereto.Similarly, description box 1422B shows the schematic for electrode array1406B, with capacitor bank 1424B serving the electrode array of eightelectrodes, namely 1408B-0 to 1408B-7.

In another example, polarity assignment information encoded in the inputsignal may be received at antenna 725 and processed at RF interface1428B of controller 1421. The polarity assignment information may bedecoded and used to program the device interfaces 1420A and 1420B sothat the polarities of electrodes 1408A-0 to 1408A-7 and 1408B-0 to1408B-7 can be set according to the polarity assignment information.

Capacitor 1422 between Vcc switch 1426 and ground 1422 may storeelectrical energy for a power-on reset circuit. In case of a power-onevent, the electric charges stored in capacitor 1422 may be used toreset the polarity assignment of each electrode and to reset registerinformation on controller 1421.

FIG. 15 shows an example of an electrode assignment for the implantabledevice 1400. In this example, the Y-joint implantable device includestwo electrode arrays, namely, electrode array 1406A and 1406B. Eachelectrode array can include up to eight electrodes. However, more orless electrodes can be used for each array, or the form factor of thearray may vary. As such, the array can be comprised of a cylindricalcatheter type body with cylindrical electrodes spaced N distance apart,or may have a connector to a paddle or other flat, unidirectional devicethat contains N number of electrode pads arranged in various patterns toyield the desired effective treatment option for the stimulation of thetissue.

The electrodes on the electrode arrays 1406A and 1406B are indexedaccording to the top mapping in FIG. 15. In this mapping, the twoelectrode arrays are represented by an eight by two matrix where eachrow of the matrix represents one of the eight electrodes on one of thetwo “Y” electrode arrays. In this example, the right most electrode ismapped as electrode #0 while the left most electrode is mapped aselectrode #7. The mapping in this example is linear.

The polarity assignment for a particular electrode can be cathodic (+),anodic (−), or off. Specifically, each electrode can take on a polarityof either a source or sink, known as an anode or a cathode, or otherwisedenoted as positive or negative. Further, each electrode of each arraycan be additionally set to an on or off state, to where the circuit isfunctionally open and the electrode is left in a neural electricalstate.

In this example, electrodes #7 and #6 of the electrode array 1406A areassigned as cathodic while electrodes #7 and #6 of the electrode array1406B are assigned as anodic. Electrodes #3 to #5 of the electrodearrays 1406A and 1406B are assigned as off. Electrodes #1 and #2 of theelectrode array 1406A are assigned as anodic while electrodes #1 and #2of the electrode array 1406B are assigned as cathodic. The significanceof programming polarity for each array on a particular electrode arraywill be explained in detail below.

FIG. 16 shows an example of longitudinal currents formed betweenelectrodes of an electrode array of the Y-joint receiver. A longitudinalcurrent is a current that flows substantially parallel to thelongitudinal axis of an electrode array. The current flows from (e.g.,serving as a source) or exits at (e.g., serving as a sink) an electrodeon the electrode array. In this illustration, electrodes #3 to #5 of theelectrode arrays 1406A are assigned as cathodic while electrode #4 ofthe electrode array 1406 is assigned as anodic. As illustrated,longitudinal currents 1602A and 1602B flow from electrode #5 toelectrode #4. Current 1602A is located above electrode array 1406 whilecurrent 1602B is located below electrode array 1406. When originatingfrom electrode #5, the combined currents 1602A and 1602B may be measuredat 1 mA. Longitudinal currents 1604A and 1604B may flow from electrode#2 to electrode #4. Current 1604A is located above electrode array 1406while current 1604B is located below electrode array 1406. Whenoriginating from electrode #3, the combined currents 1602A and 1602B maybe measured at 1 mA. When currents 1602A, 1602B, 1604A, and 1604Bconverge at electrode #4, the combined currents may be measured at 2 mA.Currents 1602A, 1602B, 1604A, and 1604B can provide therapeutic reliefto excitable tissue, such as neural tissue, on their paths. This type ofelectrode configuration can be used to activate neural tissue lateral ofthe midline.

In some implementations, spatial distribution pattern of currents can befurther enriched by the introduction of multiple electrode arrays. FIG.17A shows an example of lateral currents formed between electrodes oftwo electrode arrays of the Y-joint receiver. A lateral current is acurrent that flows in a direction substantially transverse to alongitudinal axis of the electrode array. The current either originatesfrom or exits at an electrode on the electrode array. In thisillustration, electrode #3 of electrode array 1406A is assigned ascathodic while electrode #3 of electrode array 1406B is assigned asanodic. Currents 1702A and 1704B flow from electrode #3 of electrodearray 1406A to electrode #3 of electrode array 1406B. Traversing themidline, currents 1702A and 1704B are located on mirrored paths.Originating at electrode #3 of electrode array 1406A and ending atelectrode #3 on electrode array 1406B, the combined currents 1702A and1702B are measured at 1 mA. Currents 1702A and 1704B can providetherapeutic relief to excitable tissue, such as neural tissue, on theirpaths. This electrode configuration can stimulate neural tissue closerto the midline with a horizontally oriented electrical field across theepidural space.

FIG. 17B shows an example of a combination of lateral current field andlongitudinal current field formed between electrodes of two electrodearrays of a Y-joint receiver. In this illustration, electrode #3 ofelectrode array 1406A is assigned as anodic while electrode #5 ofelectrode array 1406A and electrode #4 of electrode array 1406B areassigned as cathodic. Longitudinal currents 1704A and 1704B flow fromelectrode #5 of electrode array 1406A to electrode #3 of electrode array1406A. Meanwhile, lateral currents 1706A and 1706B flow from electrode#4 of electrode array 1406B to electrode #3 of electrode array 1406A.Longitudinal current 1704A is located above electrode array 1406A whilelongitudinal current 1704B is located below electrode array 1406A. Whenoriginating from electrode #5, the combined currents 1702A and 1702B maybe measured at 1 mA. Traversing the midline, currents 1706A and 1706Bare located on mirrored paths. When originating from electrode #4, thecombined currents 1706A and 1706B may be measured at 1 mA. When currents1704A, 1704B, 1706A, and 1706B converge at electrode #3 of electrodearray 1406, the combined currents may be measured at 2 mA. Currents1704A, 1704B, 1706A, and 1706B can provide therapeutic relief toexcitable tissue, such as neural tissue, on their paths.

As disclosed herein, configurations of the electrodes' polarity can beset from the external controller 1402 to determine a particularelectrodes combination to activate the tissue at a desired zone. In oneexample, the user interface on external controller 1402 to set thepolarity and the power state for each electrode of the array can be inthe form of a matrix interface. In this example, the matrix at theinterface can be filled in by the operator for each of the N electrodesthrough a touch-screen. Once the matrix values are set, the operatorinitiates a data transfer to the central stem of the Y-joint implantabledevice. Circuits 1408 on board central stem 1404 may receive the data asthe 8×2 matrix and store the data in self-contained memory. Whenelectrical energy in the input signal has been harvested to power theY-joint implant, the polarity to all those electrodes can be setaccording to this data in self-contained memory. In another example, theuser interface on external controller 1402 may enable an operator toalter/modify the polarity setting for a particular electrode on a givenarray individually. In particular, the polarity setting of one electrodemay be updated from the user interface on external controller 1402without transmitting information concerning the polarity setting ofother electrodes. In these examples, external controller 1402 isconfigured to transmit the input signal at least 12 cm, under an outerskin surface of the patient through tissue to the target site.

FIG. 17C shows an example of stimulation zones formed by current fieldsbetween electrodes of two electrode arrays of the Y-joint receiver. Eachstimulation zone is formed by virtue of electric field within the zonereaching an activation potential to cause neural activity. The electricfield generated in-situ depends on electrical current as well as theimpedance of the underlying tissue. The electrical current may includecontributions from both longitudinal currents and lateral currents. Astimulation zone may also be known as a focal zone. Stimulation zonesmay be formed near an electrode, such as stimulation zones 1708A, 1708Band 1708F. Stimulation zones may also be formed away from theelectrodes, for example, near mid-line, as illustrated by stimulationzones 1708C, 1708D, and 1708E.

A longitudinal current may also be formed between two electrode arrays,as illustrated by FIG. 17D. In this example, electrode arrays 1406A and1406B are placed such that the distal ends are facing each other. Suchplacement may be achieved when the two electrode arrays form a loop, orwhen one electrode array is bent to tilt towards the other. In thisdemonstrative example, longitudinal currents 1710G and 1710H flow fromelectrode #2 on electrode array 1406A to electrode #7 on electrode array1406B. Electrode #2 on electrode array 1406A is assigned as cathodicwhile electrode #7 on electrode array 1406B is assigned as anodic.Longitudinal current 1710G flows on top of the electrode arrays whilelongitudinal current 1710H flows underneath the electrode arrays.Originating at electrode #2 on electrode array 1406A, the combinedstrength of longitudinal currents 1710G and 1710H may be measured at 1mA. Exiting at electrode #7 on electrode array 1406B, the combinedstrength of longitudinal currents 1710G and 1710H may be measured at 1mA.

For various stimulation therapies, two or more devices may be to beplaced in the epidural space where the electrodes from each electrodearray can generate an electric field from one contact on one electrodearray to another contact on the other electrode array. Two generalscenarios may be noteworthy for placing the electrode arrays of thedisclosed Y-joint implantable device. In one scenario, the electrodearrays may be placed at the same spinal level, and they are separatedlaterally by a few millimeters. The electrode arrays are ideally offsetfrom the physiological midline by the same distance. FIGS. 17A to 17Ccorrespond to this scenario. In contrast, in another scenario such ashigh-frequency sub-threshold stimulation, the two electrode arrays maybe placed head to tail and aligned with the anatomical midline, wherethe combination of the two electrode arrays mimic a single longelectrode array with twice the number of contacts. FIG. 17D correspondsto this latter scenario.

The implantation procedure for the Y-joint receiver disclosed herein mayinclude the use of stylets or cannulas, as discussed below. FIG. 18Ashows an example of an implantable device with a Y-joint receiver inwhich the stylet lumen for each electrode array exits at the centralstem of the Y-joint receiver. As illustrated, stylet 1802A is beingplaced into stylet lumen 1804A at the central stem 1404 of implantabledevice 1800. Stylet lumen 1804A runs through central stem 1404 whichalso houses circuit 1408, as discussed above. Stylet 1804A extends intobranch stem 1414A and becomes stylet lumen 1806A. Stylet lumen 1806Aruns through the branch stem 1414A and exits at tip 1416A. The branchstem 1414A includes electrode array 1406A with eight electrodes, namely1406A-0 to 1406A-7, as illustrated. Likewise, stylet 1802B is beingplaced into stylet lumen 1804B at the central stem 1404 of implantabledevice 1800. Stylet lumen 1804B runs through central stem 1404 andextends into branch stem 1414B to become stylet lumen 1806B. Styletlumen 1806B runs through the branch stem 1414B and exits at tip 1416B.This branch stem 1414B includes an electrode array 1406B with eightelectrodes, namely 1406B-0 to 1406B-7, as illustrated.

FIG. 18B shows an example of an implantable device with a Y-jointreceiver in which stylet lumens for each electrode array exit at therespective stem and before the central stem of the Y-joint receiver. Inthis example, the stylet lumens 1806A and 1806B exit the respectivebranch stems 1414A and 1414B before they reach central stem 1404. Asillustrated, stylet 1802A is being placed into stylet lumen 1806A whichruns through branch stem 1414A and exits at tip 1416A. Similarly, stylet1802B is being placed into style lumen 1806B which runs through branchstem 1414B and exits at tip 1416B.

In the above examples, the inserted stylets may serve as guide wires torender the branch stems of the implantable device suitably rigid duringimplantation, such as, for example, through a needle device or anintroducer device. Once an example implantable device 1800 has beenplaced in position, the stylets can be withdrawn from the stylet lumens.Thereafter, the implanted implantable device 1800 may be anchored tosurrounding tissues, for example, by utilizing suturing features on tips1416A, 1416B, and 1418.

In addition to the use of stylets, cannulas may be used duringimplantation of the implantable device disclosed herein. FIG. 19A showsan example of a large mouth cannula to fit both the electrode arrays ofan implantable device. As illustrated, branch stems houses the electrodearrays 1406A and 1406B are inserted into big mouth cannula 1900 throughopening 1904 on the proximal side. The electrode arrays 1406A and 1406Bmay be pushed through channel 1902 and then exit big mouth cannula 1900through opening 1906 at the distal end. Once the electrodes on theelectrode arrays 1406A and 1406B have been placed in proximity of anexcitable tissue, such as a neural tissue, implantable device 1400 maybe anchored to the surrounding tissue. In some instances, suturingfeatures at tips 1416A, 1416B and 1418 may be utilized during theanchoring procedure. In these instances, prior to suturing, big mouthcannula 1900 may be withdrawn from the central stem of implantabledevice 1400.

FIG. 19B shows examples of two cannulas for the electrode arrays of animplantable device with a Y-joint receiver. As illustrated, branch stem1414A houses the electrode arrays 1406A is inserted into peel-awaycannula 1900A through opening 1906A on the proximal side. As disclosedherein, branch stem 1414A also houses cable 1412A that connects theelectrode array 1406A to a circuit 1408 on central stem 1404. Theelectrode array 1406A may be pushed through channel 1902A and then exitpeel-away cannula 1900A through opening 1906A at the distal end. Oncethe electrodes on the electrode array 1406A has been placed in proximityof an excitable tissue, such as a neutral tissue, branch stem 1414A maybe anchored to the surrounding tissue. In some instances, suturingfeatures at tip 1416A may be utilized during the anchoring procedure. Inthese instances, prior to suturing, peel-away cannula 1900A may bewithdrawn from the branch stem 1414A of implantable device 1400. In oneinstance, peel-away cannula 1900A may be torn apart and stripped offbranch stem 1414A.

Likewise, branch stem 1414B houses the electrode arrays 1406B which maybe inserted into peel-away cannula 1900B through opening 1906B on theproximal side. Branch stem 1414B also houses cable 1412B that connectsthe electrode array 1406B to circuit 1408 on central stem 1404. Theelectrode array 1406B may be pushed through channel 1902B to exitpeel-away cannula 1900A via opening 1906B at the distal end. Once theelectrodes on the electrode array 1406B have been placed in proximity ofan excitable tissue, such as a neutral tissue, branch stem 1414B may beanchored to the surrounding tissue. In some instances, suturing featuresat tip 1416B may be utilized during the anchoring procedure. In theseinstances, prior to suturing, peel-away cannula 1900B may be withdrawnfrom the branch stem 1414B of implantable device 1400. In one instance,peel-away cannula 1900B may be torn apart and stripped off branch stem1414B for the electrode arrays of an example implantable deviceaccording to some implementations.

While using the example peel-way cannulas for an implantation procedure,the peel-away action may be subsequent to both branch stems being placedinto proximity of the excitable tissue. In a similar vein, anchoring maytake place when both branch stems have been stripped off the peel-awaycannulas. In these instances, suturing features on tips 1416A, 1416B,and 1418 can be utilized for anchoring implantable device 1400 tosurrounding tissues.

A number of implementations have been described. Nevertheless, it willbe understood that various modifications may be made. Accordingly, otherimplementations are within the scope of the following claims.

What is claimed is:
 1. An implantable wirelessly powered device forimplantation in a patient's body, the device comprising: two or moreelectrode arrays configured to apply one or more electrical pulses to anexcitable tissue of the patient's body, each of the two or moreelectrode arrays including at least one electrode; two or more connectorcontacts respectively, integrally wired to the two or more electrodearrays and configured to drive the at least one electrode of each of thetwo or more electrode arrays integrally wired thereto with the one ormore electrical pulses and to set a polarity for the at least oneelectrode of each of the two or more electrode arrays integrally wiredthereto; two or more branches respectively housing the two or moreelectrode arrays and the two or more connector contacts; a central stemto which the two or more branches are integrally connected, the two ormore branches and the two or more connector contacts converging at thecentral stem at first ends of the two or more branches, and the two ormore branches being spaced apart from one another at second ends of thetwo or more branches that are disposed opposite the first ends, suchthat the two or more electrode arrays, respectively housed on the two ormore branches that are integrally connected to the central stem, can bepositioned independently of one another at two or more differentlocations on the excitable tissue that are spaced laterally apart fromone another; a first antenna configured to: receive, from a secondantenna and through electrical radiative coupling, an input signalcontaining electrical energy and polarity assignment information, thesecond antenna located outside of the patient's body; and one or morecircuits electrically connected to the first antenna and to the two ormore connector contacts, the one or more circuits configured to: createthe one or more electrical pulses suitable for stimulation of theexcitable tissue solely using the electrical energy contained in theinput signal; program each of the two or more connector contacts to setthe polarity for the at least one electrode of each of the two or moreelectrode arrays integrally wired thereto based on the polarityassignment information contained in the input signal; and supply the oneor more electrical pulses to the two or more connector contacts.
 2. Theimplantable device of claim 1, wherein the central stem on theimplantable device houses the one or more circuits and the firstantenna.
 3. The implantable device of claim 2, wherein the one or morecircuits housed in the central stem are further configured to: determineaddress electrode information from the polarity assignment information,the address electrode information indicating a destination electrode forwhich the polarity assignment information is intended; and program aparticular connector contact of the two or more connector contacts inaccordance with the determined address electrode information.
 4. Theimplantable device of claim 1, wherein the two or more connectorcontacts converge to form a Y-shape.
 5. The implantable device of claim1, wherein each of the two or more electrode arrays includes a styletlumen.
 6. The implantable device of claim 5, wherein the stylet lumen ofeach of the two or more electrode arrays extends to the central stem. 7.The implantable device of claim 1, wherein the two or more electrodearrays are configured to be implanted apart from each other inside ofthe patient's body.
 8. The implantable device of claim 7, wherein thetwo or more electrode arrays are configured to be implanted bilaterallyand are further configured to form a lateral current in the excitabletissue and between the two or more electrode arrays when the one or moreelectrical pulses are applied at the at least one electrode, the atleast one electrode set at the programmed polarity.
 9. The implantabledevice of claim 7, wherein the two or more electrode arrays areconfigured to be implanted bilaterally and are further configured toform a longitudinal current in the excitable tissue when the one or moreelectrical pulses are applied at the at least one electrode, the atleast one electrode set at the programmed polarity.
 10. The implantabledevice of claim 7, wherein the two or more electrode arrays areconfigured to be implanted longitudinally and are further configured toform a longitudinal current in the excitable tissue and between the twoor more electrode arrays when the one or more electrical pulses areapplied at the two or more electrode arrays, the at least one electrodeset at the programmed polarity.
 11. The implantable device of claim 1,wherein the two or more electrode arrays comprise at least one recordingelectrode configured to sense neural activity of the patient.
 12. Theimplantable device of claim 11, wherein the one or more circuits arefurther configured to generate a recorded electrical signal encoding thesensed neural activity.
 13. The implantable device of claim 11, whereinthe first antenna is further configured to transmit the recordedelectrical signal to the second antenna using the electrical energycontained in the input signal.
 14. The implantable device of claim 1,wherein the two or more electrode arrays include two (2) to twenty four(24) electrodes, each of the two or more electrode arrays having alongitudinal length between 0.25 mm and 6.0 mm and a diameter between0.1 mm and 0.8 mm.
 15. The implantable device of claim 14, wherein thetwo to twenty four electrodes are spaced between 1 mm to 6 mm apart andhave a combined surface area of between 0.06 mm² to 60.00 mm².
 16. Theimplantable device of claim 1, wherein the implantable device has aheight between 0.1 mm and 0.8 mm, and a width between 0.5 mm and 0.8 mm.17. The implantable device of claim 1, wherein the implantable device isshaped concavely to secure a lateral position on the excitable tissueafter the implantable device has been delivered into the patient's body.18. The implantable device of claim 1, wherein each of the two or morebranches includes a tissue anchoring feature such that the two or morebranches can be respectively secured to the excitable tissue at the twoor more different locations.
 19. The implantable device of claim 1,wherein an integral connection between the two or more branches and thecentral stem is configured such that the two or more electrode arrays,respectively housed on the two or more branches, can be delivered to theexcitable tissue simultaneously.
 20. A system for neural stimulation,comprising an implantable wirelessly powered device for implantation ina patient's body, the device comprising: two or more electrode arraysconfigured to apply one or more electrical pulses to an excitabletissue, each of the two or more electrode arrays including at least oneelectrode; two or more connector contacts respectively, integrally wiredto the two or more electrode arrays and configured to drive the at leastone electrode of each of the two or more electrode arrays integrallywired thereto with the one or more electrical pulses and to set apolarity for the at least one electrode of each of the two or moreelectrode arrays integrally wired thereto; two or more branchesrespectively housing the two or more electrode arrays and the two ormore connector contacts; a central stem to which the two or morebranches are integrally connected, the two or more branches and the twoor more connector contacts converging at the central stem at first endsof the two or more branches, and the two or more branches being spacedapart from one another at second ends of the two or more branches thatare disposed opposite the first ends, such that the two or moreelectrode arrays, respectively housed on the two or more branches thatare integrally connected to the central stem, can be positionedindependently of one another at two or more different locations on theexcitable tissue that are spaced laterally apart from one another; afirst antenna configured to: receive, from a second antenna and throughelectrical radiative coupling, an input signal containing electricalenergy and polarity assignment information, the second antenna locatedoutside of the patient's body; and one or more circuits electricallyconnected to the first antenna and to the two or more connectorcontacts, the one or more circuits configured to: create the one or moreelectrical pulses suitable for stimulation of the excitable tissuesolely using the electrical energy contained in the input signal;program each of the two or more connector contacts to set the polarityfor the at least one electrode of each of the two or more electrodearrays integrally wired thereto based on the polarity assignmentinformation contained in the input signal; and supply the one or moreelectrical pulses to the two or more connector contacts.
 21. The systemof claim 20, further comprising an exterior controller module outsidethe patient's body, the exterior controller module comprising the secondantenna configured to transmit the input signal to the implantabledevice via the electrical radiative coupling, the input signalcomprising electrical energy and polarity assignment information. 22.The system of claim 21, wherein the external controller furthercomprises a user interface to enable a user to edit the polarityassignment information for the two or more electrode arrays.
 23. Thesystem of claim 22, wherein the user interface enables the user to editthe polarity assignment information for a particular electrode the twoor more electrode arrays.
 24. The system of claim 22, wherein thepolarity assignment information includes a positive polarity, a negativepolarity, and a disconnected state.
 25. The system of claim 21, whereinthe external controller further comprises a user interface to enable auser to edit the polarity assignment information for all electrodes onthe two or more electrode arrays.
 26. The system of claim 21, whereinthe second antenna is configured to transmit the input signal via theelectrical radiative coupling at a transmission frequency from 300 MHzto 6 GHz.